Deprecate `describeEnum`. (#125016)

Final part of https://github.com/flutter/flutter/issues/123346.

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

@@ -2262,14 +2262,12 @@ class IterableProperty<T> extends DiagnosticsProperty<Iterable<T>> {
   }
 }
 
-/// An property than displays enum values tersely.
+/// [DiagnosticsProperty] that has an [Enum] as value.
 ///
-/// The enum value is displayed with the class name stripped. For example:
+/// The enum value is displayed with the enum name stripped. For example:
 /// [HitTestBehavior.deferToChild] is shown as `deferToChild`.
 ///
-/// This class can be used with classes that appear like enums but are not
-/// "real" enums, so long as their `toString` implementation, in debug mode,
-/// returns a string consisting of the class name followed by the value name. It
+/// This class can be used with enums and returns the enum's name getter. It
 /// can also be used with nullable properties; the null value is represented as
 /// `null`.
 ///
@@ -2277,7 +2275,7 @@ class IterableProperty<T> extends DiagnosticsProperty<Iterable<T>> {
 ///
 ///  * [DiagnosticsProperty] which documents named parameters common to all
 ///    [DiagnosticsProperty].
-class EnumProperty<T> extends DiagnosticsProperty<T> {
+class EnumProperty<T extends Enum?> extends DiagnosticsProperty<T> {
   /// Create a diagnostics property that displays an enum.
   ///
   /// The [level] argument must also not be null.
@@ -2293,7 +2291,7 @@ class EnumProperty<T> extends DiagnosticsProperty<T> {
     if (value == null) {
       return value.toString();
     }
-    return describeEnum(value!);
+    return value!.name;
   }
 }
 
@@ -2975,11 +2973,16 @@ String describeIdentity(Object? object) => '${objectRuntimeType(object, '<optimi
 ///
 /// void validateDescribeEnum() {
 ///   assert(Day.monday.toString() == 'Day.monday');
+///   // ignore: deprecated_member_use
 ///   assert(describeEnum(Day.monday) == 'monday');
 ///   assert(Day.monday.name == 'monday'); // preferred for real enums
 /// }
 /// ```
 /// {@end-tool}
+@Deprecated(
+  'Use the `name` getter on enums instead. '
+  'This feature was deprecated after v3.10.0-1.1.pre.'
+)
 String describeEnum(Object enumEntry) {
   if (enumEntry is Enum) {
     return enumEntry.name;