SF: Update the sequence of operation for frame rate override

This change will freeze the timeline with the new rate generated
through the requestDisplayMode before updating the render rate for
frameRateOverride

BUG: 343603085
Test: atest libsurfaceflinger_unittest
Flag: com.android.graphics.surfaceflinger.flags.vrr_bugfix_dropped_frame
Change-Id: I4d1c8febe1203de11046f6b6f4a92dc5f29cfbb3