[skshaper] Stage "Split off SkUnicode specific code"

The objective is to move SkShaper::MakeSkUnicodeBidiRunIterator into its
own file. To land this requires setting everything up to build both with
and without the new target, updating users to use the new target, then
moving the code.

Change-Id: I28091525677a9b31ee6dc60e5bb7a94d487132d8
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/757817
Reviewed-by: Kevin Lubick <kjlubick@google.com>
Commit-Queue: Kevin Lubick <kjlubick@google.com>
Commit-Queue: Ben Wagner <bungeman@google.com>
Auto-Submit: Ben Wagner <bungeman@google.com>
6 files changed