* [ios][macos] test remove source in use
* [android] test remove source in use
* [core] check source usage before remove
* [core] ensure layer::accept works with non-void return values on gcc
* [android] - remove upgrade runtime exceptions (#9191)
This reverses #3095. Rationale:
* We're now exposing source attributes as a public API. Making those attributes unavailable at certain times complicates that API.
* We're preparing to split RenderSource out of Source. Removing this removes a point of coupling between the two.