Revert "analyzer: separate unused_element_parameter from unused_element"

This reverts commit c1976b0.

Reason for revert: It seems this change caused failures on Flutter
HHH bot. Example log can be found at [0]:
```
| lib/src/super_reader/super_reader.dart:615:14: Error: Final field 'showDebugLeaderBounds' is not initialized.
| Try to initialize the field in the declaration or in every constructor.
|   final bool showDebugLeaderBounds;
|              ^^^^^^^^^^^^^^^^^^^^^

```
Looking at the sources it seems that may be related to the
`// ignore: unused_element` analyzer directive:

```
   602	/// A [SuperReaderDocumentLayerBuilder] that builds a [SelectionLeadersDocumentLayer], which positions
   603	/// leader widgets at the base and extent of the user's selection, so that other widgets
   604	/// can position themselves relative to the user's selection.
   605	class _SelectionLeadersDocumentLayerBuilder implements SuperReaderDocumentLayerBuilder {
   606	  const _SelectionLeadersDocumentLayerBuilder({
   607	    required this.links,
   608	    // ignore: unused_element
   609	    this.showDebugLeaderBounds = false,
   610	  });
   611
   612	  /// Collections of [LayerLink]s, which are given to leader widgets that are
   613	  /// positioned at the selection bounds, and around the full selection.
   614	  final SelectionLayerLinks links;
   615
   616	  /// Whether to paint colorful bounds around the leader widgets, for debugging purposes.
   617	  final bool showDebugLeaderBounds;
```

So tentatively reverting this CL.

[0] https://logs.chromium.org/logs/dart/buildbucket/cr-buildbucket/8739650477551803313/+/u/Run_customer_testing_tests/stdout

Original change's description:
> analyzer: separate unused_element_parameter from unused_element
>
> Fixes #49025
>
> This allows users to blanket ignore unused_element_parameter without
> ignoring unused_element. They are reported in distinct situations so it
> is valid to separate them.
>
> Tested: Presubmit CI
> Cq-Include-Trybots: luci.dart.try:flutter-analyze-try,analyzer-win-release-try,pkg-win-release-try
> Change-Id: I4844a6a0e0a67cd5e37ed8735b1526e174deb950
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/378500
> Reviewed-by: Brian Wilkerson <[email protected]>
> Reviewed-by: Phil Quitslund <[email protected]>
> Commit-Queue: Samuel Rawlins <[email protected]>
> Reviewed-by: Ryan Macnak <[email protected]>

Change-Id: Ibbba75fe56601c7c4b5535c9142cf94c2dd80b91
Cq-Include-Trybots: luci.dart.try:flutter-analyze-try,analyzer-win-release-try,pkg-win-release-try
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/380460
Commit-Queue: Martin Kustermann <[email protected]>
Bot-Commit: Rubber Stamper <[email protected]>
Reviewed-by: Slava Egorov <[email protected]>

Author: mkustermann

pkg/analysis_server/test/src/services/correction/assist/convert_class_to_enum_test.dart

@@ -348,7 +348,7 @@ base class E {
 class _E {
   static const _E c = _E();
 
-  // ignore: unused_element_parameter, recursive_constant_constructor
+  // ignore: unused_element, recursive_constant_constructor
   const _E({_E e = const _E()});
 }
 ''');

pkg/analyzer/lib/src/error/codes.g.dart

@@ -7585,9 +7585,11 @@ class WarningCode extends AnalyzerErrorCode {
   ///  Parameters:
   ///  0: the name of the parameter that is declared but not used
   static const WarningCode UNUSED_ELEMENT_PARAMETER = WarningCode(
-    'UNUSED_ELEMENT_PARAMETER',
+    'UNUSED_ELEMENT',
     "A value for optional parameter '{0}' isn't ever given.",
     correctionMessage: "Try removing the unused parameter.",
+    hasPublishedDocs: true,
+    uniqueName: 'UNUSED_ELEMENT_PARAMETER',
   );
 
   ///  Parameters:

pkg/analyzer/messages.yaml

@@ -27308,6 +27308,8 @@ WarningCode:
       kinds of declarations are analyzed:
       - Private top-level declarations and all of their members
       - Private members of public declarations
+      - Optional parameters of private functions for which a value is never
+        passed
 
       Not all references to an element will mark it as "used":
       - Assigning a value to a top-level variable (with a standard `=`
@@ -27327,26 +27329,6 @@ WarningCode:
       class [!_C!] {}
       ```
 
-      #### Common fixes
-
-      If the declaration isn't needed, then remove it.
-
-      If the declaration is intended to be used, then add the code to use it.
-  UNUSED_ELEMENT_PARAMETER:
-    problemMessage: "A value for optional parameter '{0}' isn't ever given."
-    correctionMessage: Try removing the unused parameter.
-    hasPublishedDocs: false
-    comment: |-
-      Parameters:
-      0: the name of the parameter that is declared but not used
-    documentation: |-
-      #### Description
-
-      The analyzer produces this diagnostic when a value is never passed for an
-      optional parameter declared within a private declaration.
-
-      #### Example
-
       Assuming that no code in the library passes a value for `y` in any
       invocation of `_m`, the following code produces this diagnostic:
 
@@ -27371,6 +27353,14 @@ WarningCode:
       ```
 
       If the declaration is intended to be used, then add the code to use it.
+  UNUSED_ELEMENT_PARAMETER:
+    sharedName: UNUSED_ELEMENT
+    problemMessage: "A value for optional parameter '{0}' isn't ever given."
+    correctionMessage: Try removing the unused parameter.
+    hasPublishedDocs: true
+    comment: |-
+      Parameters:
+      0: the name of the parameter that is declared but not used
   UNUSED_FIELD:
     problemMessage: "The value of the field '{0}' isn't used."
     correctionMessage: Try removing the field, or using it.

pkg/analyzer/tool/diagnostics/diagnostics.md

@@ -23183,6 +23183,8 @@ void f() {
 
 ### unused_element
 
+_A value for optional parameter '{0}' isn't ever given._
+
 _The declaration '{0}' isn't referenced._
 
 #### Description
@@ -23192,6 +23194,8 @@ referenced in the library that contains the declaration. The following
 kinds of declarations are analyzed:
 - Private top-level declarations and all of their members
 - Private members of public declarations
+- Optional parameters of private functions for which a value is never
+  passed
 
 Not all references to an element will mark it as "used":
 - Assigning a value to a top-level variable (with a standard `=`
@@ -23211,23 +23215,6 @@ produces this diagnostic:
 class [!_C!] {}
 ```
 
-#### Common fixes
-
-If the declaration isn't needed, then remove it.
-
-If the declaration is intended to be used, then add the code to use it.
-
-### unused_element_parameter
-
-_A value for optional parameter '{0}' isn't ever given._
-
-#### Description
-
-The analyzer produces this diagnostic when a value is never passed for an
-optional parameter declared within a private declaration.
-
-#### Example
-
 Assuming that no code in the library passes a value for `y` in any
 invocation of `_m`, the following code produces this diagnostic:
 

runtime/observatory/lib/src/elements/debugger.dart

@@ -2942,7 +2942,7 @@ class DebuggerConsoleElement extends CustomElement implements Renderable {
   DebuggerConsoleElement.created() : super.created('debugger-console');
 
   /// Is [container] scrolled to the within [threshold] pixels of the bottom?
-  // ignore: unused_element_parameter
+  // ignore: unused_element
   static bool _isScrolledToBottom(DivElement? container, [int threshold = 2]) {
     if (container == null) {
       return false;