Correct opacitiy for drag move indicator

Switching to use mirrored surface for the move indicator broke the
opacity changes of the move indicator.
This CL fixes the issue.

Bug: 418920013
Test: WMShellUnitTest
Test: go/cd-smoke
Flag: com.android.window.flags.enable_connected_displays_window_drag
Change-Id: Ibe86db0aaa6ab20ac76a27f8db9dbf09c524ffd3