Stop supporting '[this]' as a comment reference.

The analyzer does not support it and does not intend to, so this change aligns
with that effort. It makes analyzing the gap between analyzer and dartdoc
easier as well.

Fixes dart-lang#3761

Author: srawlins

CHANGELOG.md

@@ -1,6 +1,9 @@
 ## 8.0.10-dev
 
 * Un-deprecate the `--resources-dir` option.
+* Remove support for `[this]` as a comment reference. Referring to the
+  containing element can be written as `this [Foo]`, and referring to 'this'
+  can just be written as `` `this` ``.
 
 ## 8.0.9
 

lib/src/dartdoc_options.dart

@@ -572,7 +572,7 @@ abstract class DartdocOption<T extends Object?> {
   U getValueAs<U>(String name, Folder dir) =>
       _children[name]?.valueAt(dir) as U;
 
-  /// Apply the function [visit] to [this] and all children.
+  /// Apply the function [visit] to this [DartdocOption] and all children.
   void traverse(void Function(DartdocOption option) visit) {
     visit(this);
     for (var value in _children.values) {

lib/src/model/container.dart

@@ -242,7 +242,6 @@ abstract class Container extends ModelElement
             .addEntriesIfAbsent(modelElement.parameters.generateEntries());
       }
     }
-    referenceChildren['this'] = this;
     return referenceChildren;
   }();
 

test/end2end/model_test.dart

@@ -2742,9 +2742,6 @@ void main() async {
                 doAwesomeStuff, 'BaseForDocComments.aNonDefaultConstructor'),
             equals(MatchingLinkResult(aNonDefaultConstructor)));
 
-        expect(referenceLookup(doAwesomeStuff, 'this'),
-            equals(MatchingLinkResult(baseForDocComments)));
-
         expect(referenceLookup(doAwesomeStuff, 'value'),
             equals(MatchingLinkResult(doAwesomeStuffParam)));