ICU optimization

Mainly rearranging the code to perform all ICU iterations once
and cache the results for the next text layouts.

Change-Id: I2c2a502c705510eb169bf62efbfcc13b658591e3
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/293336
Commit-Queue: Julia Lavrova <jlavrova@google.com>
Reviewed-by: Ben Wagner <bungeman@google.com>
9 files changed