CodeGen. Generate members of most leaf AstNodeImpl classes.

Every declaration annotated with `@generated` was generated. In the
current version there are `2180` such declarations. For comparison,
there are `2167` instances of `@override` in total, and `@generated +
@override` has `1576` instances, so we generate `72%` of all overrides.

The generator automatically formats and sorts `ast.dart` after applying
changes, so the result is nice and clean. We run a separate DAS instance
from the script to do this.

Things to improve in the future:

1. Generate for non-leaf classes.

2. Support for `DoNotGenerate`.

Change-Id: I05e6356c9aac68449d5117ad8fd533735f130c73
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/427481
Reviewed-by: Brian Wilkerson <[email protected]>
Commit-Queue: Konstantin Shcheglov <[email protected]>
Reviewed-by: Paul Berry <[email protected]>

Author: scheglov

pkg/analysis_server/lib/src/computer/computer_highlights.dart

@@ -912,7 +912,6 @@ class _DartUnitHighlightsComputerVisitor extends RecursiveAstVisitor<void> {
   @override
   void visitConstructorSelector(ConstructorSelector node) {
     computer._addRegion_node(node.name, HighlightRegionType.CONSTRUCTOR);
-    node.visitChildren(this);
   }
 
   @override