WM: Mark screen rotation layer as opaque

When rotating the device, if the screenshot of the display is not
opaque, the user might see other layers appear through
the screenshot. This will look like ghost images. We fix this
by marking the layer as opaque.

Test: rotate homescreen with The Mandalorian wallpaper
Fixes: 191128850

Change-Id: I5b1e7bb2ff028bfe5f6dd31929ddf58f0f7a1a78