Changed the way refresh rate is changed

The previous method for requesting display mode changes was unreliable, as SurfaceFlinger could disregard the request. The newer approach, modifying the render rate directly (as implemented in FrameRateOverrideCtsActivity.java), is significantly more dependable, although still not perfectly consistent.

Bug: 402781340
Test: atest DisplayEventTest
Flag: EXEMPT test change

Change-Id: I72aa639047f3043d28bc0ad8ab14193ec8dc427a