Allow signature apps to obtain REPOSITION_SELF_WINDOWS

OEMs may be interested in using this API to provide better user
experiences for their first party apps.

Bug: 407607317
Test: Builds
Flag: com.android.window.flags.enable_window_repositioning_api
Change-Id: I0d66cef9408309b14812d55c3924de322c43dfaa
1 file changed