Currently we only show the widget preview if dart.experimentalFlutterWidgetPreview is set and flutterCapabilities.supportsWidgetPreview (Flutter SDK is >= 3.36.0-1).

We should remove the requirement for the experiment flag for a version of the SDK that has all the fixes we think are necessary before showing this by default (by implementing a new capability flutterCapabilities.supportsWidgetPreviewByDefault).

I think flutter/flutter#175783 is the most significant fix, so we could gate it on the version that lands in, which would mean any subsequent beta branch would have it enabled by default (@bkonyi - does this seem good to you, or are there any other changes/fixes you think we should require?).

(fyi @jwren @anderdobo)