Reland "Revert "hide nested hinting enum""

This reverts commit f49563bf9276f70441fd22da83413d585b2bcc17.

Reason for revert: Google3 also.

Original change's description:
> Revert "Revert "hide nested hinting enum""
> 
> This reverts commit 6bd19df9fa9d26d9de4de646b2cdf82ff5dca67c.
> 
> Restores original CL, but adds guards for flutter.
> 
> Bug: skia:
> Change-Id: I380b4ea87d293355026d734249aa2b8c397da144
> Reviewed-on: https://skia-review.googlesource.com/c/169345
> Reviewed-by: Florin Malita <fmalita@chromium.org>
> Commit-Queue: Mike Reed <reed@google.com>
> Auto-Submit: Mike Reed <reed@google.com>

TBR=fmalita@chromium.org,reed@google.com

Change-Id: I26a07555df56ce92e86b114ecf4ab64643e71ed1
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: skia:
Reviewed-on: https://skia-review.googlesource.com/c/169441
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
29 files changed