Make unfocused windows in pinned mode unable to receive touch input

Make unfocused ActivityStacks in pinned windowing mode ignore input on
Leanback devices (TVs).

Bug: 144032975
Bug: 153050065
Test: atest atest CtsWindowManagerDeviceTestCases:PinnedStackTests
Change-Id: Id9049c543ed6493a840b7a34a68f4e7bc1010262