RESTRICT AUTOMERGE: Backport When an opaque window has alpha < 0.5, don't let it receive touches.

When a window is declared as opaque but the alpha is low, it's likely a fadeout animation or other visual change that should not affect touch handling.

Bug: 266433089
Test: inputflinger_tests
Flag: EXEMPT BUGFIX
Cherrypick-From: https://googleplex-android-review.googlesource.com/q/commit:61b3b73116cb7fc760683db1d02e6466522aacbf
Merged-In: I9ba48365d0ea080a4e68c8c497049225b759df79
Change-Id: I9ba48365d0ea080a4e68c8c497049225b759df79