Add bar type window caption.

This is the first CL towards implementing the bar type caption which
will have a back button, a handle, and a close button. The caption will
also disappear when the attached task is not in focus.
Still to be implemented:
1: Windowing options appearing on handle click
2: Drag down in fullscreen to enter desktop mode
3: Caption display via hovering when cursor available

Bug: 239960071
Test: Manual: confirm new caption displays with the correct buttons/layout.
Confirm buttons work and focus change works with multiple tasks.
Test: Atest WindowDecorationTests

Change-Id: I2ebed76b803d1f337edc3e7340966909f63eaf40