Minor doc updates (#62008)

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

@@ -77,6 +77,12 @@ abstract class Listenable {
 ///
 /// This interface is implemented by [ValueNotifier<T>] and [Animation<T>], and
 /// allows other APIs to accept either of those implementations interchangeably.
+///
+/// See also:
+///
+///  * [ValueListenableBuilder], a widget that uses a builder callback to
+///    rebuild whenever a [ValueListenable] object triggers its notifications,
+///    providing the builder with the value of the object.
 abstract class ValueListenable<T> extends Listenable {
   /// Abstract const constructor. This constructor enables subclasses to provide
   /// const constructors so that they can be used in const expressions.

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

@@ -30,11 +30,17 @@ BuildContext _getParent(BuildContext context) {
   return parent;
 }
 
-/// A class representing a particular configuration of an action.
+/// A class representing a particular configuration of an [Action].
 ///
 /// This class is what a key map in a [ShortcutMap] has as values, and is used
 /// by an [ActionDispatcher] to look up an action and invoke it, giving it this
 /// object to extract configuration information from.
+///
+/// See also:
+///
+///  * [Actions.invoke], which invokes the action associated with a specified
+///    [Intent] using the [Actions] widget that most tightly encloses the given
+///    [BuildContext].
 @immutable
 class Intent with Diagnosticable {
   /// A const constructor for an [Intent].

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

@@ -1814,10 +1814,12 @@ abstract class SingleChildRenderObjectWidget extends RenderObjectWidget {
 /// storage for that child list, it doesn't actually provide the updating
 /// logic.)
 ///
-/// This will return a [RenderObject] mixing in [ContainerRenderObjectMixin],
-/// which provides the necessary functionality to visit the children of the
-/// container render object (the render object belonging to the [children] widgets).
-/// Typically, this is a [RenderBox] with [RenderBoxContainerDefaultsMixin].
+/// Subclasses must return a [RenderObject] that mixes in
+/// [ContainerRenderObjectMixin], which provides the necessary functionality to
+/// visit the children of the container render object (the render object
+/// belonging to the [children] widgets). Typically, subclasses will return a
+/// [RenderBox] that mixes in both [ContainerRenderObjectMixin] and
+/// [RenderBoxContainerDefaultsMixin].
 ///
 /// See also:
 ///

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

@@ -31,6 +31,9 @@ typedef LayoutWidgetBuilder = Widget Function(BuildContext context, BoxConstrain
 /// The [builder] function is _not_ called during layout if the parent passes
 /// the same constraints repeatedly.
 /// {@endtemplate}
+///
+/// Subclasses must return a [RenderObject] that mixes in
+/// [RenderConstrainedLayoutBuilder].
 abstract class ConstrainedLayoutBuilder<ConstraintType extends Constraints> extends RenderObjectWidget {
   /// Creates a widget that defers its building until layout.
   ///