clean up drawTextUTF8 and rename to textToGlyphRunList

Pull out the glyph positioning code in anticipations of removing
simplifyDrawText.

This is part of a larger CL:
https://skia-review.googlesource.com/c/skia/+/388719

Change-Id: I935fd91f70d708a7a30785b6eea8e4e7c1f9c739
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/392416
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Herb Derby <herb@google.com>
4 files changed