Fix numerous cases of casting away const

Stop disabling cast-qual, to keep us honest.
I tried to fix these correctly wherever I could. Many were easy. On a
few I had to punt and const_cast, but now those serve as a reminder that
we're doing something fishy -- which is the point of having an explicit
name for that operation.

By far the most sketchy thing here is in SkBlitter.cpp ... two blitters
ignore the const on the aa and runs, then mutate them. I have no idea
how that's safe. :shrug:

Change-Id: I42e13a17c4631cd9b4d3f59dcf605a2295675339
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/780001
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
64 files changed