Clean up #includes in SkCFObject.

SKCFObject.h wasn't compiling without prefixing it with other includes,
so adding them into the actual file itself. Also changed to use the
more generic __APPLE__ as a guard rather than BUILD_FOR_MAC or
BUILD_FOR_IOS defines, and added the file to BUILD.gn so it will be
added to Xcode projects.

Change-Id: I67a48d0156ef1eb5c69dd045f0acadf147053eb6
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/455163
Auto-Submit: Jim Van Verth <jvanverth@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
2 files changed