Mark private types as invalid in the public symbol table.

Previously, in public code, private types didn't exist anywhere in the
symbol table chain, and those names were free for the taking. Now, we
register them as invalid types in the public symbol table. This prevents
them from being used as variable names, and gives a more explicit error
if you try to use them as a type.

Change-Id: I9a943bf923639b72cbf36b1acf4b4fbe70982786
Bug: skia:12538
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/459119
Commit-Queue: John Stiles <johnstiles@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
25 files changed