Fix doc comment references to 'this' (flutter#150379)

Work towards dart-lang/dartdoc#3761

Sibling CL to https://dart-review.googlesource.com/c/sdk/+/365204

The analyzer has never recognized `[this]` as a valid doc comment
reference (and the `comment_references` lint rule has similarly
reported such reference attempts). dartdoc has its own algorithms
for resolving comment references, which we are dismantling in favor
of a single resolution, provided by the analyzer.

We've also decided against adding support in the analyzer (see
https://github.com/dart-lang/linter/issues/2079), so these
reference attempts should be re-written.

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [ ] I listed at least one issue that this PR fixes in the description
above.
- [ ] I updated/added relevant documentation (doc comments with `///`).
- [ ] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [x] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel
on [Discord].

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Author: srawlins

packages/flutter/lib/src/rendering/object.dart

@@ -3325,8 +3325,8 @@ abstract class RenderObject with DiagnosticableTreeMixin implements HitTestTarge
   /// tree as this [RenderObject], as the behavior is undefined.
   ///
   /// This method ignores [RenderObject.paintsChild]. This means it will still
-  /// try to compute the paint transform even if [this] or `target` is currently
-  /// not visible.
+  /// try to compute the paint transform even if this [RenderObject] or
+  /// `target` is currently not visible.
   ///
   /// If `target` is null, this method returns a matrix that maps from the
   /// local paint coordinate system to the coordinate system of the

packages/flutter/lib/src/semantics/semantics.dart

@@ -3878,9 +3878,8 @@ class SemanticsConfiguration {
   /// This is a request to increase the value represented by the widget. For
   /// example, this action might be recognized by a slider control.
   ///
-  /// If [this.value] is set, [increasedValue] must also be provided and
-  /// [onIncrease] must ensure that [this.value] will be set to
-  /// [increasedValue].
+  /// If [value] is set, [increasedValue] must also be provided and
+  /// [onIncrease] must ensure that [value] will be set to [increasedValue].
   ///
   /// VoiceOver users on iOS can trigger this action by swiping up with one
   /// finger. TalkBack users on Android can trigger this action by pressing the
@@ -3897,9 +3896,8 @@ class SemanticsConfiguration {
   /// This is a request to decrease the value represented by the widget. For
   /// example, this action might be recognized by a slider control.
   ///
-  /// If [this.value] is set, [decreasedValue] must also be provided and
-  /// [onDecrease] must ensure that [this.value] will be set to
-  /// [decreasedValue].
+  /// If [value] is set, [decreasedValue] must also be provided and
+  /// [onDecrease] must ensure that [value] will be set to [decreasedValue].
   ///
   /// VoiceOver users on iOS can trigger this action by swiping down with one
   /// finger. TalkBack users on Android can trigger this action by pressing the
@@ -4812,11 +4810,11 @@ class SemanticsConfiguration {
     _setFlag(SemanticsFlag.isReadOnly, value);
   }
 
-  /// Whether [this.value] should be obscured.
+  /// Whether [value] should be obscured.
   ///
   /// This option is usually set in combination with [isTextField] to indicate
   /// that the text field contains a password (or other sensitive information).
-  /// Doing so instructs screen readers to not read out [this.value].
+  /// Doing so instructs screen readers to not read out [value].
   bool get isObscured => _hasFlag(SemanticsFlag.isObscured);
   set isObscured(bool value) {
     _setFlag(SemanticsFlag.isObscured, value);
@@ -4844,7 +4842,7 @@ class SemanticsConfiguration {
   }
 
   /// The currently selected text (or the position of the cursor) within
-  /// [this.value] if this node represents a text field.
+  /// [value] if this node represents a text field.
   TextSelection? get textSelection => _textSelection;
   TextSelection? _textSelection;
   set textSelection(TextSelection? value) {