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>
8 files changed