Reland "make enum santizer fatal"

This is a reland of 166dbd3135e02d0e874591db02f9b1ad7fc961f5

Since last attempt,
   - update SkPath::Direction docs
   - kIllegal is not an advanced blend mode

Original change's description:
> make enum santizer fatal
>
> This enum sanitizer checks that all the values of the enum we use fall
> within the range of the enumerated values.
>
> The main thing this helps point out is that the size of enum types in
> C++ need only be large enough to hold the largest declared value; larger
> values are undefined.  In practice, most enums are implemented as ints
> for compatibility with C, so while this hasn't pointed out anything
> egregiously broken, the sanitizer has found a couple possibly dangerous
> situations in our codebase.
>
> For most types using values outside the enum range, we can just
> explicitly size them to int.  This makes their de facto size de jure.
>
> But we need to actually make GrBlendEquation and GrBlendCoeff not store
> values outside their enumerated range.  They're packed into bitfields
> that really can't represent those (negative) values.  So for these I've
> added new kIllegal values to the enums, forcing us to deal with our
> once-silent illegal values a bit more explicitly.
>
> Change-Id: Ib617694cf1aaa83ae99289e9e760f49cb6393a2f
> Reviewed-on: https://skia-review.googlesource.com/c/168484
> Reviewed-by: Brian Osman <brianosman@google.com>

Cq-Include-Trybots: skia.primary:Housekeeper-PerCommit-Bookmaker,Test-Android-Clang-AndroidOne-GPU-Mali400MP2-arm-Debug-All-Android
Change-Id: Id93b80bbeae11872542c9b76715e3c3cb10609fd
Reviewed-on: https://skia-review.googlesource.com/c/168582
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
15 files changed