Remove use of ICU C++ API from SkParagraph.

This is mostly about consolidating and removing use of
icu::UnicodeString. It was used mostly as an intermediary for
conversion, and the new conversions should make one fewer copy of the
data.

Change-Id: I1d0e5f0dc21c47ed7c80f456b9129c4c9a36b09a
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/292718
Reviewed-by: Mike Reed <reed@google.com>
Reviewed-by: Julia Lavrova <jlavrova@google.com>
Commit-Queue: Ben Wagner <bungeman@google.com>
10 files changed