Improve SkArc ergonomics, use it everywhere but SkCanvas

(Not changing the virtual onDrawArc, thanks to clients deriving from
SkCanvas). Otherwise, this tries to use SkArc wherever it makes sense,
and adds explicit types (rather than the confusing `useCenter` bool).

Change-Id: I1f89b2a412cb6b070ab36612eb9f7ed8518f6ade
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/846187
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
19 files changed