Reland "Switching SkText to UTF16"

This is a reland of a3262aa1d25eb31f118ee395a0ecae83fd0e27b6

Original change's description:
> Switching SkText to UTF16
>
> Required some changes in SkUnicode to support it
> SkShaper still works on UTF8
>
> Change-Id: I76645668e1d9bf95eb4539a066deea2b24ecf5e9
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/406360
> Reviewed-by: Julia Lavrova <jlavrova@google.com>
> Commit-Queue: Julia Lavrova <jlavrova@google.com>

Change-Id: Ib21898d4acda8ab78e5e6fd1c7b9b0da41c3fa83
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/407396
Reviewed-by: Julia Lavrova <jlavrova@google.com>
Commit-Queue: Julia Lavrova <jlavrova@google.com>
8 files changed