Screen capture: Guard screen recording button behind feature flag

The radio button which allows the user to switch between screen
recording and screenshots shouldn't show if the screen recording feature
flag is not enabled.

Bug: 434700644
Test: Manual
Flag: com.android.systemui.large_screen_recording
Change-Id: Ie8d62f29f440c8c6e7e74fd9d4d46531a03b2250