`FakeView` wraps the same underlying `FlutterView`. Sending semantics updates and Scene objects from multiple fake views into the same engine `FlutterView` violates contracts with the engine. This PR stubs out `render` and `updateSemantics` methods in `FakeView` classes to prevent that.

This unblocks https://github.com/flutter/engine/pull/48251, which implements multi-view semantics for web.