Add DEFER_RESUME_FOCUS_IN_NON_FOCUSED_WINDOW to DesktopExperienceFlags.

This flag controls whether focus is deferred during resume for
non-focused windows in desktop mode.

Flag: EXEMPT exposing defer_resume_focus_in_non_focused_window aconfig
Bug: 438781414
Change-Id: I3ce5aa6fb759be2588556563221af4911a77cd10