Add info strings to code blocks. (#146085)

In preparation to add the lint
`missing_code_block_language_in_doc_comment`, added info strings to a
bunch of fenced code blocks.

Related to issue: https://github.com/dart-lang/linter/issues/4904

## 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.
- [X] I updated/added relevant documentation (doc comments with `///`).
- [X] 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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[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
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[Features we expect every widget to implement]:
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[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
[Data Driven Fixes]:
https://github.com/flutter/flutter/wiki/Data-driven-Fixes

dev/benchmarks/macrobenchmarks/lib/src/web/recorder.dart

@@ -164,7 +164,7 @@ abstract class Recorder {
 ///
 /// Example:
 ///
-/// ```
+/// ```dart
 /// class BenchForLoop extends RawRecorder {
 ///   BenchForLoop() : super(name: benchmarkName);
 ///
@@ -219,7 +219,7 @@ abstract class RawRecorder extends Recorder {
 ///
 /// Example:
 ///
-/// ```
+/// ```dart
 /// class BenchDrawCircle extends SceneBuilderRecorder {
 ///   BenchDrawCircle() : super(name: benchmarkName);
 ///
@@ -311,7 +311,7 @@ abstract class SceneBuilderRecorder extends Recorder {
 ///
 /// Example:
 ///
-/// ```
+/// ```dart
 /// class BenchListView extends WidgetRecorder {
 ///   BenchListView() : super(name: benchmarkName);
 ///

dev/benchmarks/test_apps/stocks/lib/i18n/stock_strings.dart

@@ -21,7 +21,7 @@ import 'stock_strings_es.dart';
 /// localizationDelegates list, and the locales they support in the app's
 /// supportedLocales list. For example:
 ///
-/// ```
+/// ```dart
 /// import 'i18n/stock_strings.dart';
 ///
 /// return MaterialApp(
@@ -36,7 +36,7 @@ import 'stock_strings_es.dart';
 /// Please make sure to update your pubspec.yaml to include the following
 /// packages:
 ///
-/// ```
+/// ```yaml
 /// dependencies:
 ///   # Internationalization support.
 ///   flutter_localizations:

dev/devicelab/lib/framework/browser.dart

@@ -426,7 +426,7 @@ class BlinkTraceEvent {
   ///
   /// Sample event encoded as JSON (the data is bogus, this just shows the format):
   ///
-  /// ```
+  /// ```json
   /// {
   ///   "name": "myName",
   ///   "cat": "category,list",

dev/tools/dartdoc_checker.dart

@@ -41,7 +41,7 @@ const List<String> dartdocDirectiveCanaryFiles = <String>[
 /// sample code where the sequence is perfectly legal, e.g. for required named
 /// parameters of a method:
 ///
-/// ```
+/// ```dart
 /// void foo({@required int bar});
 /// ```
 void checkForUnresolvedDirectives(Directory dartDocDir) {

dev/tools/localization/bin/gen_date_localizations.dart

@@ -31,14 +31,14 @@ String? currentLocale;
 ///
 /// The following outputs the generated Dart code to the console as a dry run:
 ///
-/// ```
+/// ```bash
 /// dart dev/tools/localization/bin/gen_date_localizations.dart
 /// ```
 ///
 /// If the data looks good, use the `--overwrite` option to overwrite the
 /// lib/src/l10n/date_localizations.dart file:
 ///
-/// ```
+/// ```bash
 /// dart dev/tools/localization/bin/gen_date_localizations.dart --overwrite
 /// ```
 Future<void> main(List<String> rawArgs) async {

packages/flutter_tools/lib/src/base/async_guard.dart

@@ -31,7 +31,7 @@ import 'dart:async';
 /// Rationale:
 ///
 /// Consider the following snippet:
-/// ```
+/// ```dart
 /// try {
 ///   await foo();
 ///   ...
@@ -55,7 +55,7 @@ import 'dart:async';
 /// [asyncGuard] is intended to wrap awaited expressions occurring in a `try`
 /// block. The behavior described above gives the behavior that users
 /// intuitively expect from `await`. Consider the snippet:
-/// ```
+/// ```dart
 /// try {
 ///   await asyncGuard(() async {
 ///     var c = Completer();

packages/flutter_tools/lib/src/commands/attach.dart

@@ -40,19 +40,19 @@ import '../vmservice.dart';
 ///
 /// With an application already running, a HotRunner can be attached to it
 /// with:
-/// ```
+/// ```bash
 /// $ flutter attach --debug-url http://127.0.0.1:12345/QqL7EFEDNG0=/
 /// ```
 ///
 /// If `--disable-service-auth-codes` was provided to the application at startup
 /// time, a HotRunner can be attached with just a port:
-/// ```
+/// ```bash
 /// $ flutter attach --debug-port 12345
 /// ```
 ///
 /// Alternatively, the attach command can start listening and scan for new
 /// programs that become active:
-/// ```
+/// ```bash
 /// $ flutter attach
 /// ```
 /// As soon as a new VM Service is detected the command attaches to it and

packages/flutter_tools/lib/src/localizations/gen_l10n.dart

@@ -692,7 +692,7 @@ class LocalizationsGenerator {
   /// Whether to generate the Dart localization methods with named parameters.
   ///
   /// If this sets to true, the generated Dart localization methods will be:
-  /// ```
+  /// ```dart
   /// String helloWorld({required String name});
   /// ```
   final bool useNamedParameters;