Fix includes of SkRRect and other Skia headers

I would like to (re-)land https://skia-review.googlesource.com/c/skia/+/512158
which tidies up includes around SkRRect. I searched for all
places in libs/hwui that used SkRRect and made sure they either
forward declared it or included it, as appropriate.

While going through these files, I fixed a few other includes that
stood out to me, e.g. SkPaint, SkCanvas, etc to make sure the files
that use the symbols are the ones including them (and lessening
transitive dependencies).

Change-Id: I44792a6b9f06a54d052cefa4cbc9342f46ab2a4f