Support a Primary and a Floating ActionMode in DecorView.

This CL modifies the support for a single ActionMode in PhoneWindow.
DecorView to support both a Primary and a Floating ActionModes
simultaneously.

Things pending after this CL:
- Handling an actual Floating ActionMode
- Cleaning up the now unused ActionModeWrapper and its related code

Change-Id: Ie2e5ec27393ce9eededadf5bc379bab39981a365