Fix some deprecation details (#136385)

This fixes/notates a few deprecations from an audit for the next tech debt cycle.

- ThemeData errorColor and backgroundColor are notated as deprecated in multiple places, but one usage had a different version tag. Updated to match the rest.
- ThemeData.copyWith useMaterial3 was deprecated because it did not do what developers expected - it did not automatically reassign all of the color values and such. (confirmed with @HansMuller) I added a note so that when we later remove it we don't introduce a bug.
- the describeEnum deprecation was tagged wrong, it was a very long PR so by the time it merged the version it was finally tagged with was much later. (https://github.com/flutter/flutter/pull/125016)

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

@@ -2948,7 +2948,7 @@ String describeIdentity(Object? object) => '${objectRuntimeType(object, '<optimi
 /// {@end-tool}
 @Deprecated(
   'Use the `name` getter on enums instead. '
-  'This feature was deprecated after v3.10.0-1.1.pre.'
+  'This feature was deprecated after v3.14.0-2.0.pre.'
 )
 String describeEnum(Object enumEntry) {
   if (enumEntry is Enum) {

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

@@ -1584,12 +1584,12 @@ class ThemeData with Diagnosticable {
     Color? selectedRowColor,
     @Deprecated(
       'Use colorScheme.error instead. '
-      'This feature was deprecated after v2.6.0-11.0.pre.',
+      'This feature was deprecated after v3.3.0-0.5.pre.',
     )
     Color? errorColor,
     @Deprecated(
       'Use colorScheme.background instead. '
-      'This feature was deprecated after v2.6.0-11.0.pre.',
+      'This feature was deprecated after v3.3.0-0.5.pre.',
     )
     Color? backgroundColor,
     @Deprecated(
@@ -1623,6 +1623,8 @@ class ThemeData with Diagnosticable {
       platform: platform ?? this.platform,
       scrollbarTheme: scrollbarTheme ?? this.scrollbarTheme,
       splashFactory: splashFactory ?? this.splashFactory,
+      // When deprecated useMaterial3 removed, maintain `this.useMaterial3` here
+      // for == evaluation.
       useMaterial3: useMaterial3 ?? this.useMaterial3,
       visualDensity: visualDensity ?? this.visualDensity,
       // COLOR