Tune RefreshRateConfigs for fractional refresh rates

This CL contains several changes in order to tune
RefrshRateConfigs for fractional refresh rates

1. TV devices support fractional refresh rates which are
within 1/1001 of an integer, for example 59.94 and 60.
This change reduces the tolerance we use when
selecting the best refresh rate, so we can differtiate
between the scores which 59.94 and 60 will get
when a layer requests 60 (or 59.94).

2. Changes the threshold in getFrameRateDivider
so it can differntiate between 59.94 and 60 fps.

3. Explicitly check if we're voting for a refresh
rate in a fractional pair when calculating the
vote for ExplicitExactOrMultiple. If so, vote with
a contant score.

4. Finally the CL changes some log lines to make
debugging easier and adds more comments.

Bug: 196404992
Bug: 196191168
Test: atest libsurfaceflinger_unittest
      atest MatchContentFrameRateTest SetFrameRateTest
Change-Id: I694e2aa5b16e9b4e0f6d1e8263b1ac35099605fd