Fix dislocated doc and comment on ThemeData localize cache (#137315)

This comment on _localizedThemeDataCacheSize was a bit garbled from getting split up, and the doc on _localizedThemeDataCache was missing from having been moved elsewhere.

It looks like the dislocation happened in 8b86d238 (#116088), which was otherwise making unrelated changes, including a couple of lines near these.  Likely it was due to an error in resolving merge or rebase conflicts at some point while revising that PR.

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

@@ -1465,13 +1465,6 @@ class ThemeData with Diagnosticable {
   Color get toggleableActiveColor => _toggleableActiveColor!;
   final Color? _toggleableActiveColor;
 
-  // The number 5 was chosen without any real science or research behind it. It
-
-  // copies of ThemeData in memory comfortably) and not too small (most apps
-  // shouldn't have more than 5 theme/localization pairs).
-  static const int _localizedThemeDataCacheSize = 5;
-  /// Caches localized themes to speed up the [localize] method.
-
   /// Creates a copy of this theme but with the given fields replaced with the new values.
   ///
   /// The [brightness] value is applied to the [colorScheme].
@@ -1708,7 +1701,14 @@ class ThemeData with Diagnosticable {
       bottomAppBarColor: bottomAppBarColor ?? _bottomAppBarColor,
     );
   }
+
+  // The number 5 was chosen without any real science or research behind it. It
   // just seemed like a number that's not too big (we should be able to fit 5
+  // copies of ThemeData in memory comfortably) and not too small (most apps
+  // shouldn't have more than 5 theme/localization pairs).
+  static const int _localizedThemeDataCacheSize = 5;
+
+  /// Caches localized themes to speed up the [localize] method.
   static final _FifoCache<_IdentityThemeDataCacheKey, ThemeData> _localizedThemeDataCache =
       _FifoCache<_IdentityThemeDataCacheKey, ThemeData>(_localizedThemeDataCacheSize);