[flutter_tools] enable single widget reload optimization by default on master (#66507)

This should be a mostly non breaking change for hot reload workflows that improves performance, but if you see anything odd with hot reload behavior on master please file a bug. This feature can also be disabled without any changes to the SDK with flutter config --no-single-widget-reload-optimization 

packages/flutter_tools/lib/src/features.dart

@@ -242,7 +242,7 @@ const Feature singleWidgetReload = Feature(
   environmentOverride: 'FLUTTER_SINGLE_WIDGET_RELOAD',
   master: FeatureChannelSetting(
     available: true,
-    enabledByDefault: false,
+    enabledByDefault: true,
   ),
   dev: FeatureChannelSetting(
     available: true,