add SkParagraph to public headers and fix warnings

Change-Id: Icb62636e96f1fecb97c4f4c918d073ab611420f3
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/302900
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Julia Lavrova <jlavrova@google.com>
3 files changed