Refactor MeasuredText

This refactoring contains:
- Add lots of comments.
- Mark private the internal fields and introduce accessors and helper
  methods.
- Factor out the auto grow array implementation to another class.
- Use SynchronizedPool for pool implementation.
- Introduce three build methods for each use case.
- Hide addStyleRun and compute all necessary informations in build method.

Locally verified that this doesn't cause performance regressions.
Here is a raw performance test result on walleye-userdebug.

StaticLayoutPerfTest (median, N=100):
createRandom:          7,846,449 -> 8,003,903 (+2.01%)
createRandom Balanced: 7,810,436 -> 7,919,200 (+1.40%)

TextViewOnMeasurePerfTest (median, N=100):
measure_AtMost:       94,276,376 ->  94,124,658 (-0.16%)
measure_Exactly:      91,629,352 ->  91,617,639 (-0.01%)
measure_Unspecified: 151,006,181 -> 150,957,598 (-0.03%)

Test: bit CtsTextTestCases:*
Test: bit CtsGraphicsTestCases:*
Test: bit CtsWidgetTestCases:*
Test: bit FrameworksCoreTests:android.text.StaticLayoutTest
Bug: 65024629

Change-Id: I58d3020a3fa560d05576e18888fbfe46e2975e8f

0 files changed, 0 insertions, 0 deletions