fix some formatting issues (#25474)

packages/flutter/lib/src/animation/tween_sequence.dart

@@ -34,7 +34,7 @@ import 'tween.dart';
 ///     ),
 ///   ],
 /// ).animate(myAnimationController);
-///```
+/// ```
 class TweenSequence<T> extends Animatable<T> {
   /// Construct a TweenSequence.
   ///

packages/flutter/lib/src/foundation/diagnostics.dart

@@ -474,7 +474,7 @@ final TextTreeConfiguration transitionTextConfiguration = TextTreeConfiguration(
 ///   <name>: <description>:
 ///     <properties>
 ///     <children>
-///```
+/// ```
 ///
 /// See also:
 ///

packages/flutter/lib/src/painting/image_provider.dart

@@ -664,7 +664,7 @@ class MemoryImage extends ImageProvider<MemoryImage> {
 /// AssetImage('icons/heart.png', scale: 1.5)
 /// ```
 ///
-///## Assets in packages
+/// ## Assets in packages
 ///
 /// To fetch an asset from a package, the [package] argument must be provided.
 /// For instance, suppose the structure above is inside a package called
@@ -690,7 +690,7 @@ class MemoryImage extends ImageProvider<MemoryImage> {
 /// lib/backgrounds/background1.png
 /// lib/backgrounds/background2.png
 /// lib/backgrounds/background3.png
-///```
+/// ```
 ///
 /// To include, say the first image, the `pubspec.yaml` of the app should specify
 /// it in the `assets` section:

packages/flutter/lib/src/painting/image_resolution.dart

@@ -105,7 +105,7 @@ const String _kAssetManifestFileName = 'AssetManifest.json';
 /// lib/backgrounds/background1.png
 /// lib/backgrounds/background2.png
 /// lib/backgrounds/background3.png
-///```
+/// ```
 ///
 /// To include, say the first image, the `pubspec.yaml` of the app should specify
 /// it in the `assets` section:

packages/flutter/lib/src/painting/text_style.dart

@@ -140,7 +140,7 @@ const String _kColorForegroundWarning = 'Cannot provide both a color and a foreg
 ///
 /// Custom fonts can be declared in the `pubspec.yaml` file as shown below:
 ///
-///```yaml
+/// ```yaml
 /// flutter:
 ///   fonts:
 ///     - family: Raleway
@@ -155,7 +155,7 @@ const String _kColorForegroundWarning = 'Cannot provide both a color and a foreg
 ///          - asset: fonts/Schyler-Regular.ttf
 ///          - asset: fonts/Schyler-Italic.ttf
 ///            style: italic
-///```
+/// ```
 ///
 /// The `family` property determines the name of the font, which you can use in
 /// the [fontFamily] argument. The `asset` property is a path to the font file,
@@ -197,7 +197,7 @@ const String _kColorForegroundWarning = 'Cannot provide both a color and a foreg
 ///
 /// Then the app can declare a font like in the example below:
 ///
-///```yaml
+/// ```yaml
 /// flutter:
 ///   fonts:
 ///     - family: Raleway
@@ -205,14 +205,14 @@ const String _kColorForegroundWarning = 'Cannot provide both a color and a foreg
 ///         - asset: assets/fonts/Raleway-Regular.ttf
 ///         - asset: packages/my_package/fonts/Raleway-Medium.ttf
 ///           weight: 500
-///```
+/// ```
 ///
 /// The `lib/` is implied, so it should not be included in the asset path.
 ///
 /// In this case, since the app locally defines the font, the TextStyle is
 /// created without the `package` argument:
 ///
-///```dart
+/// ```dart
 /// const TextStyle(fontFamily: 'Raleway')
 /// ```
 ///

packages/flutter/lib/src/widgets/page_storage.dart

@@ -29,7 +29,7 @@ import 'framework.dart';
 ///       tab: tab,
 ///     ),
 ///   }),
-///)
+/// )
 /// ```
 class PageStorageKey<T> extends ValueKey<T> {
   /// Creates a [ValueKey] that defines where [PageStorage] values will be saved.