The Low Processor Usage Mode Sleep Usec setting is now used as a
FPS limiter rather than a constant sleep duration.
This will increase CPU/GPU usage slightly due to the higher
effective FPS, but the increase in overall smoothness is worth it.
If both Force Fps and Low Processor Usage Mode settings are enabled
in the project settings, only the setting that causes the highest
sleep duration will be retained.
This closes#11030.
(cherry picked from commit 1c28b269d8)
087a83fd54
