Allow ToolbarActionBar to pass-through unhandled keyShortcuts

It was consuming all keyShortcuts which broke system hotkeys
like shift+tab.

In order to prevent the decor/phonewindow from creating menus,
this creates a dummy view in onCreatePanelView.

This also includes a change to Activity to not send KEYCODE_TAB
keystrokes to the defaulthandler. This was preventing keyboard
navigation from working on any activity that had a default
search fallback.

Bug: 32482282
Bug: 18021345
Test: Added a CTS test (ToolbarTest#testKeyShortcuts) for toolbar
      keyShortcuts. Verified Tab-navigation works in Play Store.
Change-Id: I5c732a2b21219157818bed49576debd20d5a8178