Convert refresh rate blocking zone thresholds from nits

Additionally:
- change the brightness value stored in DisplayModeDirector to float scale so that the brightness thresholds don't have to be converted to the int scale
- convert ambient thresholds to float for simplicity of code
- fix incorrect Float.NaN comparison in DPC

Bug: 290906453
Test: atest DisplayDeviceConfigTest
Test: atest DisplayModeDirectorTest
Test: atest DeviceConfigParsingUtilsTest
Test: atest DisplayPowerControllerTest
Test: atest DisplayPowerController2Test
Change-Id: I6f582109ea1c4fd4110493e716fffb6a9a882bba