FloatingToolbar: Support for menu groups.

1. Menu groups are now separated by dividers
2. Update to menu item spacing as specified in new UX mocks
3. TextView-Editor now passes the "assist" menu as a group
4. "Share" menu reordered after "Cut/Copy/Paste" as per UX mocks update.

Test: Manual tests.
Bug: 34777048
Bug: 34777833
Change-Id: I3d435d8a38e5b146a54706f12dbf3ff629c504bf