Don't allow pinned window to be IME target

SysUi's PIP window (PipMenuActivity) is always focusable,
transparent and yet never should be an IME target.

Bug: 158881678
Test: atest WindowStateTests#testCanBeImeTarget
Change-Id: Ie863dd1037d0c446f35a8b1ec07c18efaddb1840
2 files changed