[DDC] Provide metadata to help filter JS scopes for debugging

[grouma]

In package:dwds we manually filter out the two outer most scopes:
https://github.com/dart-lang/webdev/blob/446fb9d63875a765fa3704c71ed76ede61a51325/dwds/lib/src/debugging/dart_scope.dart#L23

This is brittle and can be broken given changes to the root bootstrap logic. I will soon update the logic to filter scopes until we find where the Dart SDK is defined. This will be done by looking for core and dart on a JS scope. Although a bit better, this too seems brittle.

It'd be great if DDC provided metadata to help determine if a scope should be considered for debugging.

[annagrin]

We can name all the library closures with some special name, detectable from the debugger, and only display the scopes that come after the scope with that name.

This requires exposing scope name in WipScope class though - see google/webkit_inspection_protocol.dart#56