Hide ICU C++ API from Skia users.

Parts of third_party need the C++ API so hide it from Skia users as
needed to prevent re-introduction.

This also avoids the ICU version renaming / name mangling when building
our own test version of ICU. This makes life in an editor and debugger
much easier.

Reviewed-on: https://skia-review.googlesource.com/c/skia/+/292854
Reviewed-by: Julia Lavrova <jlavrova@google.com>
Commit-Queue: Ben Wagner <bungeman@google.com>
Change-Id: Id636fbf9e750fe72a4ace8a59fb9acac839a07c4
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/292967
Reviewed-by: Ben Wagner <bungeman@google.com>
6 files changed