Enable ClangTidy check readability-static-accessed-through-instance.

Our codebase generally tends to avoid this pattern naturally, and this
can catch real mistakes, e.g. http://review.skia.org/308659

https://clang.llvm.org/extra/clang-tidy/checks/readability-static-accessed-through-instance.html

Change-Id: I3b37ab6242bcca310bbbec718facdd8687f9c4ff
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/308658
Commit-Queue: John Stiles <johnstiles@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
7 files changed