Launch Taskbar All Apps with Meta key when it's available.

Taskbar All Apps will be chosen over Launcher's when we are in an app or
in overview. Otherwise, we fallback to toggling Launcher All Apps.

Test: Manual, adb shell input keyevent 117
Fix: 282111244
Flag: ENABLE_ALL_APPS_SEARCH_IN_TASKBAR
Change-Id: I68e4cb3a80d42e233f7d9ad33fc3791b5c75d219