Enforce IWYU on SkPicture-related files

This also puts Slug.h behind #ifdefs in SkRecorder.cpp and
SkPicturePlayback.cpp

As the buffet build progresses, we'll have to work out a way
to build with slugs in a way that does not require #ifdefs.

Change-Id: I43e701c2c647a0401dbc8fd88d6b6ed8948f63fc
Bug: skia:14136, skia:13052
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/655819
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Kevin Lubick <kjlubick@google.com>
7 files changed