Fix IME window can't show on keyguard with setShowWhenLocked.

For new API android:showWhenLocked and Activity#setShowWhenLocked
has a bug that didn't sync window side, caused IME target window will
still be treated no show when locked flag in
PhoneWindowManager#shouldBeHiddenByKeyguard() and then the IME window
will be hidden.

Thanks to AM / WM unification, leverage this to call
ActivityRecord#canShowWhenLocked in WM side rather then just checking
FLAG_SHOW_WHEN_LOCKED.

Bug: 119629545
Test: atest KeyguardLockedTests
Change-Id: I59b01c24b54fb512c5ef4c107274fc36bb3c948e