Floating Toolbars: Wrap the ActionMode creation in DecorView

This change will allow us to create ActionMode representations on the
fly after onCreateActionMode by using the Decorator pattern. The new
ActionModeWrapper will be responsible for the creating the
appropriate ActionMode depending on the type chosen by the client,
and setting it up.

Things pending that are NOT addressed by this CL:
- ActionModes created by callback.onWindowStartingActionMode(). This
includes all current usages in an existing ActionBar, as it is
handled by Activity. This requires some additional refactoring.
- Representing the floating type
- Moving the view creation code specific to StandaloneActionMode
from DecorView to ActionModeWrapper, decoupling DecorView from
StandaloneActionMode completely
- Supporting two ActionModes in parallel in DecorView, one of each type

Change-Id: I1a8db711f53b771eac74f0e6496106acf1ca2727