Create mipmaps when creating images

Follow-on CLs:
- add serialization for mips to pictures
- implement for other image types (e.g. lazy(?), gpu)
- improve generated mip quality

Bug: skia:10411
Change-Id: Id874f170e9cb8ae4405dc4f6249e1ea6274f20aa
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/297739
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
12 files changed