Prevent meta shortcut from cancelling split select state.

There are two things that need to be changed for this to work:

1. Make the isInOverview condition check for any Overview UI (including
   the split select state, modal, etc.)
2. Toggle Home All Apps directly, because firing the intent will cause
   Launcher to pause and resume before the intent is handled. We
misinterpret the pause as a request to cancel split screen. Since
TaskbarManager has a reference to Launcher, we might as well call the
method directly.

Test: Manual
Fix: 319076403
Flag: N/A
Change-Id: Ib8899188f593a168a054a16717df4a95be098557