SurfaceFlinger: introduce PhaseOffsetsAsDurations

Currently we define phase offset for each refresh rate. This works for
<= 2 refresh rates, but doesn't scale well. This change is introducing
a new way to calculate phase offsets, which is based on duration. Then,
based on the duration and refresh rate, a phase offset is calculated.

The calculation is captured here: https://docs.google.com/spreadsheets/d/1a_5cVNY3LUAkeg-yL56rYQNwved6Hy-dvEcKSxp6f8k/edit#gid=0

Bug: 145561086
Bug: 141329414
Test: jank tests
Test: adb shell /data/nativetest64/libsurfaceflinger_unittest/libsurfaceflinger_unittest
Change-Id: I16aaf7437d30c4b12f955bdaac36582dd100519f