Add migration guide for accentColor changes

Provide a URL for extended information on handling migration related to accent color changes.
diff --git a/packages/flutter/lib/src/material/theme_data.dart b/packages/flutter/lib/src/material/theme_data.dart
index 17814e3..521a721 100644
--- a/packages/flutter/lib/src/material/theme_data.dart
+++ b/packages/flutter/lib/src/material/theme_data.dart
@@ -225,12 +225,16 @@
     Color? primaryColorLight,
     Color? primaryColorDark,
     @Deprecated(
-      'Use colorScheme.secondary instead. '
+      'Use colorScheme.secondary instead. For more information, consult the '
+      'migration guide at '
+      'https://flutter.dev/docs/release/breaking-changes/theme-data-accent-properties#migration-guide. '
       'This feature was deprecated after v2.3.0-0.1.pre.',
     )
     Color? accentColor,
     @Deprecated(
-      'No longer used by the framework, please remove any reference to it. '
+      'No longer used by the framework, please remove any reference to it. For more information, consult the '
+      'migration guide at '
+      'https://flutter.dev/docs/release/breaking-changes/theme-data-accent-properties#migration-guide. '
       'This feature was deprecated after v2.3.0-0.1.pre.',
     )
     Brightness? accentColorBrightness,
@@ -281,7 +285,9 @@
     TextTheme? textTheme,
     TextTheme? primaryTextTheme,
     @Deprecated(
-      'No longer used by the framework, please remove any reference to it. '
+      'No longer used by the framework, please remove any reference to it. For more information, consult the '
+      'migration guide at '
+      'https://flutter.dev/docs/release/breaking-changes/theme-data-accent-properties#migration-guide. '
       'This feature was deprecated after v2.3.0-0.1.pre.',
     )
     TextTheme? accentTextTheme,