Add a new entry point for making promise images

This paves the way for promise image sharing among direct & recording
contexts, and untethers promise images from DDL recorder.

Followup CLs will migrate us to actually use this entry point,
and then migrate Chrome to do same.

Bug: skia:10286
Change-Id: I0ad46e8e4b91d8bc03cb039b304d2ea6d8a65c35
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/373716
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
12 files changed