Include WindowManager owners in core/res/OWNERS

Resources used in WindowManager Core are added to frameworks/base/core/res/ so we often run into problem where WindowManager owners can't fully approve CLs that have trivial changes in resource files.

Bug: 262439469
Change-Id: Ifdf283aed9b7803ca403bec2e5c21c3dfcc4e824
Test: manual
1 file changed