[ci no changelog needed]
This PR implements a new helper for the future Component Browser - `component_group::multi::Wrapper`. It propagates FRP events from multiple component groups and ensures that only a single component group is focused at all times.
See the updated component group demo scene (console logs shows propagated FRP events from all component groups):
https://user-images.githubusercontent.com/6566674/172359141-8ea6f1ba-e357-4c1b-852a-adb4d5207e03.mp4
- Fixed a `define_endpoints_2!` macro. FRP endpoints for `focus` events weren't connected properly.
- List View now uses an overlay shape to catch mouse events, it allows much easier implementation of `is_header_selected` in the component group.
