Hook up to-float menu-item in desktop

This hooks up the to-float menu-item to bubbles-enter
in the desktop handle menu behind a flag.

The bubbles impl is currently a no-op.

Bug: 384976265
Test: enable bubbles-anything and see menu-item
Flag: com.android.wm.shell.enable_bubble_anything
Change-Id: I84a0d6a87ed9bdd9983845d56dcdc58c03e72f3c