[Inspector V2] Implementation widgets erroneously included in widget tree [package:stager]

[elliette]

I noticed when running the Property Editor, many widgets from the Flutter framework are being erroneously being considered widgets created by the local project, and therefore being included in the widget tree even when implementation widgets are hidden.

I don't see the same behavior when running DevTools itself, and my best guess why this is occurring is because we are running the Property Editor as a stager app.

Note: The implementation widgets are also included in the summary tree of the legacy inspector, so this is not unique to the new inspector.

[elliette]

I think this is because we were launching the property editor from DevTools root, and not from the packages/devtools_app. Launching from devtools_app resolves this.

[elliette]

Found related but separate issue for widget preview integration, filed #8807

[elliette]

See comment here: #8806 (comment)