Correct SF frame interval.

When SF fps doesn't match vsync rate (either due to vrr or frame rate
override), the frame interval calculation in Scheduler should take this
into account.

Bug: 328352850
Test: atest CtsSurfaceControlTests
Test: atest libsurfaceflinger_unittest
Test: atest FrameRateOverrideTest
Change-Id: I3261c7f2245fcb64c3e79bb3dcb21f1b0e44a395