Screen capture: Require one feature flag to be enabled

Both the `new_screen_record_toolbar` and `desktop_screen_capture`
feature flags show a new UI for screen capture. However the flags target
different screen sizes. Only require one of the flags to be enabled to
show the new UI, and so that each flag can follow a different release
timeline.

Bug: 433749229
Test: Manual
Flag: com.android.systemui.desktop_screen_capture
Change-Id: I3cfe2207a2dd1df951dcff1f0672503b64dab480