Enforce IWYU on skottie and sksg

While using these modules in G3, I ran into a few cases where missing
#includes caused problems, so I decided to enforce IWYU on the
entirety of both modules.

A few non-Skottie files also needed updating as a result or in
unrelated but similar errors.

Change-Id: I453afd156291136dc8d9acebb68512a78eb64e36
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/818104
Auto-Submit: Kevin Lubick <kjlubick@google.com>
Reviewed-by: Florin Malita <fmalita@google.com>
Commit-Queue: Kevin Lubick <kjlubick@google.com>
156 files changed