[Java.Interop.Tools.Cecil] remove System.Linq in IsSubclassOf

[jonathanpeppers]

Using the Mono profiler, I found:

Allocation summary
    Bytes      Count  Average Type name
  7636736      59662      128 System.Func<Mono.Cecil.TypeDefinition,System.Boolean>
  3685952      57593       64 Java.Interop.Tools.Cecil.TypeDefinitionRocks.<GetTypeAndBaseTypes>d__3

The stack traces of these are from:

2498944 bytes from:
    Xamarin.Android.Tasks.GenerateJavaStubs:Run (Java.Interop.Tools.Cecil.DirectoryAssemblyResolver)
    Xamarin.Android.Tasks.ManifestDocument:Merge (Microsoft.Build.Utilities.TaskLoggingHelper,Java.Interop.Tools.Cecil.TypeDefinitionCache,System.Collections.Generic.List`1<Mono.Cecil.TypeDefinition>,string,bool,string,System.Collections.Generic.IEnumerable`1<string>)
    Xamarin.Android.Tasks.ManifestDocument:GetGenerator (Mono.Cecil.TypeDefinition,Java.Interop.Tools.Cecil.TypeDefinitionCache)
    Java.Interop.Tools.Cecil.TypeDefinitionRocks:IsSubclassOf (Mono.Cecil.TypeDefinition,string,Java.Interop.Tools.Cecil.TypeDefinitionCache)
    (wrapper alloc) object:ProfilerAllocSmall (intptr,intptr)
    (wrapper managed-to-native) object:__icall_wrapper_mono_profiler_raise_gc_allocation (object)
...
1273344 bytes from:
    Xamarin.Android.Tasks.ManifestDocument:Merge (Microsoft.Build.Utilities.TaskLoggingHelper,Java.Interop.Tools.Cecil.TypeDefinitionCache,System.Collections.Generic.List`1<Mono.Cecil.TypeDefinition>,string,bool,string,System.Collections.Generic.IEnumerable`1<string>)
    Xamarin.Android.Tasks.ManifestDocument:GetGenerator (Mono.Cecil.TypeDefinition,Java.Interop.Tools.Cecil.TypeDefinitionCache)
    Java.Interop.Tools.Cecil.TypeDefinitionRocks:IsSubclassOf (Mono.Cecil.TypeDefinition,string,Java.Interop.Tools.Cecil.TypeDefinitionCache)
    Java.Interop.Tools.Cecil.TypeDefinitionRocks:GetTypeAndBaseTypes (Mono.Cecil.TypeDefinition,Java.Interop.Tools.Cecil.TypeDefinitionCache)
    (wrapper alloc) object:ProfilerAllocSmall (intptr,intptr)
    (wrapper managed-to-native) object:__icall_wrapper_mono_profiler_raise_gc_allocation (object)

This IsSubclassOf method gets called ~40K times during a build:

Method call summary
Total(ms) Self(ms)      Calls Method name
     2431      117      43493 Java.Interop.Tools.Cecil.TypeDefinitionRocks:IsSubclassOf (Mono.Cecil.TypeDefinition,string,Java.Interop.Tools.Cecil.TypeDefinitionCache)

Reviewing IsSubclassOf we can just remove the System.Linq usage and
use a foreach loop instead.

The results of building the Xamarin.Forms integration project on
Windows:

Before:
559 ms  GenerateJavaStubs                          1 calls
After:
535 ms  GenerateJavaStubs                          1 calls

A ~24ms savings is pretty good for a small app.

I suspect it would have even better improvements on macOS / Mono, due
to what I saw in: dotnet/android#4260