Bump DartDoc to 8.0.0 (#139088)

Bumping DartDoc to 8.0.0. https://pub.dev/packages/dartdoc/changelog

Will be also removing the `@hideConstantImplementations` directive since
the behaviour is default now.
See issue https://github.com/dart-lang/dartdoc/issues/3564.

## 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].
- [X] 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] All existing and new tests are passing.

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

<!-- Links -->
[Contributor Guide]:
https://github.com/flutter/flutter/wiki/Tree-hygiene#overview
[Tree Hygiene]: https://github.com/flutter/flutter/wiki/Tree-hygiene
[test-exempt]:
https://github.com/flutter/flutter/wiki/Tree-hygiene#tests
[Flutter Style Guide]:
https://github.com/flutter/flutter/wiki/Style-guide-for-Flutter-repo
[Features we expect every widget to implement]:
https://github.com/flutter/flutter/wiki/Style-guide-for-Flutter-repo#features-we-expect-every-widget-to-implement
[CLA]: https://cla.developers.google.com/
[flutter/tests]: https://github.com/flutter/tests
[breaking change policy]:
https://github.com/flutter/flutter/wiki/Tree-hygiene#handling-breaking-changes
[Discord]: https://github.com/flutter/flutter/wiki/Chat

dev/bots/docs.sh

@@ -111,7 +111,7 @@ function generate_docs() {
     # Install and activate dartdoc.
     # When updating to a new dartdoc version, please also update
     # `dartdoc_options.yaml` to include newly introduced error and warning types.
-    "$DART" pub global activate dartdoc 7.0.2
+    "$DART" pub global activate dartdoc 8.0.0
 
     # Install and activate the snippets tool, which resides in the
     # assets-for-api-docs repo:

packages/flutter/lib/src/cupertino/icons.dart

@@ -59,7 +59,6 @@ import 'package:flutter/widgets.dart';
 /// See also:
 ///
 ///  * [Icon], used to show these icons.
-/// {@hideConstantImplementations}
 @staticIconProvider
 abstract final class CupertinoIcons {
   /// The icon font used for Cupertino icons.

packages/flutter/lib/src/material/icons.dart

@@ -149,7 +149,6 @@ final class PlatformAdaptiveIcons implements Icons {
 ///  * [IconButton]
 ///  * <https://material.io/resources/icons>
 ///  * [AnimatedIcons], for the list of available animated Material Icons.
-/// {@hideConstantImplementations}
 @staticIconProvider
 abstract final class Icons {
   /// A set of platform-adaptive Material Design icons.