[Android][libraries] TimeZoneInfo Android imp (#54845)

Fixes #41867

Android has removed zone.tab, so TimeZoneInfo.Unix.cs will no longer work properly on Android as GetTimeZoneIds directly depends on the zone.tab file. The chain of dependency is as follows
 
GetSystemTimeZones -> PopulateAllSystemTimeZones -> GetTimeZoneIds -> zone.tab
                TZI.cs                                  TZI.Unix.cs                        TZI.Unix.cs         TZI.Unix.cs
 Where TZI is TimeZoneInfo

zone.tab is a file that is found on the unix system under /usr/share/zoneinfo/
GetTimeZoneIds reads zone.tab to obtain the TimeZoneId in that file
PopulateAllSystemTimeZones caches all the TimeZone Ids in cachedData
GetSystemTimeZones returns a ReadOnlyCollection containing all valid TimeZone’s from the local machine, and the entries are sorted by their DisplayName. It relies on cachedData._systemTimeZones being populated.

The problem is that the time zone data for Android can be found in the file tzdata at the possible locations

/apex/com.android.tzdata/etc/tz/tzdata
/apex/com.android.runtime/etc/tz/tzdata
/data/misc/zoneinfo/tzdata
/system/usr/share/zoneinfo/tzdata

The rest of unix the time zone data can be found in the file zone.tab at

 /usr/share/zoneinfo/zone.tab
Android's TimeZoneInfo implementation should read time zone data from its locations instead of the general /usr/share/zoneinfo/zone.tab path. Moreover, tzdata contains all timezones byte data.

This PR achieves the following:

1. Splits TimeZoneInfo.Unix.cs into TimeZoneInfo.Unix.cs, TimeZoneInfo.Unix.NonAndroid.cs (non-Android), and 
    TimeZoneInfo.Unix.Android.cs (Android specific)
2. Adds an interop to obtain the default time zone on Android based on persist.sys.timezone
3. Implements GetLocalTimeZoneCore TryGetTimeZoneFromLocalMachineCore and GetTimeZoneIds for Android 
    based on mono/mono implementation 
    https://github.com/mono/mono/blob/main/mcs/class/corlib/System/TimeZoneInfo.Android.cs
4. Adds new string resources to throw exceptions
5. Refactors the mono/mono implementation of parsing tzdata

Android tzdata files are found in the format of
Header <Beginning of Entry Index> Entry Entry Entry ... Entry <Beginning of Data Index> <TZDATA>

https://github.com/aosp-mirror/platform_bionic/blob/master/libc/tzcode/bionic.cpp

The header (24 bytes) contains the following information
signature - 12 bytes of the form "tzdata2012f\0" where 2012f is subject to change
index offset - 4 bytes that denotes the offset at which the index of the tzdata file starts
data offset - 4 bytes that denotes the offset at which the data of the tzdata file starts
final offset - 4 bytes that used to denote the final offset, which we don't use but will note.

Each Data Entry (52 bytes) can be used to generate a TimeZoneInfo and contain the following information
id - 40 bytes that contain the id of the time zone data entry timezone<id>
byte offset - 4 bytes that denote the offset from the data offset timezone<id> data can be found
length - 4 bytes that denote the length of the data for timezone<id>
unused - 4 bytes that used to be raw GMT offset, but now is always 0 since tzdata2014f (L).

When GetLocalTimeZoneCore TryGetTimeZoneFromLocalMachineCore or GetTimeZoneIds are called, an android timezone data instance is instantiated and loaded by attempting to load a tzdata file that can be found at four locations mentioned earlier. The file is parsed by first loading the header which contains information about where the data index and data begin. The data index is then parsed to obtain the timezone and the corresponding bytes location in the file to fill the three arrays _ids _byteOffsets _lengths. These arrays are referenced to obtain the corresponding byte data for a timezone, and functions from TimeZoneInfo.Unix.cs are leveraged to create a TimeZoneInfo from there.

Author: mdh1418

src/libraries/Common/src/Interop/Unix/System.Native/Interop.GetDefaultTimeZone.Android.cs

@@ -0,0 +1,14 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Runtime.InteropServices;
+
+internal static partial class Interop
+{
+    internal static partial class Sys
+    {
+        [DllImport(Interop.Libraries.SystemNative, EntryPoint = "SystemNative_GetDefaultTimeZone", CharSet = CharSet.Ansi, SetLastError = true)]
+        internal static extern string? GetDefaultTimeZone();
+    }
+}

src/libraries/Native/Unix/System.Native/pal_datetime.c

@@ -2,13 +2,15 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 #include "pal_config.h"
-
-#include <stdlib.h>
+#include "pal_datetime.h"
 #include <stdint.h>
-#include <time.h>
+#include <stdlib.h>
+#include <string.h>
 #include <sys/time.h>
-
-#include "pal_datetime.h"
+#if defined(TARGET_ANDROID)
+#include <sys/system_properties.h>
+#endif
+#include <time.h>
 
 static const int64_t TICKS_PER_SECOND = 10000000; /* 10^7 */
 #if HAVE_CLOCK_REALTIME
@@ -39,3 +41,18 @@ int64_t SystemNative_GetSystemTimeAsTicks()
     // in failure we return 00:00 01 January 1970 UTC (Unix epoch)
     return 0;
 }
+
+#if defined(TARGET_ANDROID)
+char* SystemNative_GetDefaultTimeZone()
+{
+    char defaulttimezone[PROP_VALUE_MAX];
+    if (__system_property_get("persist.sys.timezone", defaulttimezone))
+    {
+        return strdup(defaulttimezone);
+    }
+    else
+    {
+        return NULL;
+    }
+}
+#endif

src/libraries/Native/Unix/System.Native/pal_datetime.h

@@ -4,5 +4,10 @@
 #pragma once
 
 #include "pal_compiler.h"
+#include "pal_types.h"
 
 PALEXPORT int64_t SystemNative_GetSystemTimeAsTicks(void);
+
+#if defined(TARGET_ANDROID)
+PALEXPORT char* SystemNative_GetDefaultTimeZone(void);
+#endif

src/libraries/System.Private.CoreLib/src/Resources/Strings.resx

@@ -3802,4 +3802,16 @@
   <data name="Arg_MemberInfoNotFound" xml:space="preserve">
     <value>A MemberInfo that matches '{0}' could not be found.</value>
   </data>
+  <data name="InvalidOperation_BadTZHeader" xml:space="preserve">
+    <value>Bad magic in '{0}': Header starts with '{1}' instead of 'tzdata'</value>
+  </data>
+  <data name="InvalidOperation_ReadTZError" xml:space="preserve">
+    <value>Unable to fully read from file '{0}' at offset {1} length {2}; read {3} bytes expected {4}.</value>
+  </data>
+  <data name="InvalidOperation_BadIndexLength" xml:space="preserve">
+    <value>Length in index file less than AndroidTzDataHeader</value>
+  </data>
+  <data name="TimeZoneNotFound_ValidTimeZoneFileMissing" xml:space="preserve">
+    <value>Unable to properly load any time zone data files.</value>
+  </data>
 </root>

src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems

@@ -1958,6 +1958,9 @@
     <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.GetCwd.cs">
       <Link>Common\Interop\Unix\System.Native\Interop.GetCwd.cs</Link>
     </Compile>
+    <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.GetDefaultTimeZone.Android.cs" Condition="'$(TargetsAndroid)' == 'true'">
+      <Link>Common\Interop\Unix\System.Native\Interop.GetDefaultTimeZone.Android.cs</Link>
+    </Compile>
     <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.GetEGid.cs">
       <Link>Common\Interop\Unix\System.Native\Interop.GetEGid.cs</Link>
     </Compile>
@@ -2131,6 +2134,8 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\LowLevelMonitor.Unix.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\TimerQueue.Unix.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\TimeZoneInfo.Unix.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\TimeZoneInfo.Unix.Android.cs" Condition="'$(TargetsAndroid)' == 'true'" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\TimeZoneInfo.Unix.NonAndroid.cs" Condition="'$(TargetsAndroid)' != 'true'" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetsUnix)' == 'true'">
     <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.GetEUid.cs">