Migrate GrContextPriv & ivars to GrDirectContext

After this, GrContextPriv gets renamed and GrContext gets removed.

Change-Id: I49b034e4669876becb50b93c5fe3af887481e1ba
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/326158
Reviewed-by: Robert Phillips <robertphillips@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
Auto-Submit: Adlai Holler <adlai@google.com>
4 files changed