Create API for Launcher to signal bubble bar state

Allow Launcher to signal when bubble bar is used or not.
Previously we were relying on having an active bubble state listener to
determine if bubble bar is used.
This is causing issues during rotation when taskbar and bubble bar get
recreated. During rotation the listener gets removed from WMShell.
This triggered logic on shell side to switch back to floating bubbles.
After taskbar and bubble bar get recreated. We register a listener again
and switch back to bubble bar mode.
This switching back and forth causes unwanted UI changes.

TODO: bubbles still collapse when rotating on home screen

Bug: 357115534
Flag: com.android.wm.shell.enable_bubble_bar
Test: atest BubblesTest
Test: atest WMShellMultivalentTestsOnDevice:com.android.wm.shell.bubbles.BubbleControllerTest
Test: atest WMShellRobolectricTests:com.android.wm.shell.bubbles.BubbleControllerBubbleBarTest
Test: manual, have bubble bar expanded while in app, rotate device
Test: manual, device folded, expand bubbles, unfold, check bubble bar
  expanded
Test: manual, switch to 3-button nav, check bubble bar expanded after
  rotation when in app

Change-Id: I6ac0e672f797d60617cda27498e57f2e6c84802e