Reland "Mark GLSL reserved names as reserved in SkSL grammar."

This reverts commit 5f15c695f970f35980c859efc56843679ceded45.

Reason for revert: landed http://ag/15959743 to fix Android roll

Original change's description:
> Revert "Mark GLSL reserved names as reserved in SkSL grammar."
>
> This reverts commit 57f3fc4cde764c098666acdac05a7c905508fb2d.
>
> Reason for revert: breaking Android roll
>
> Original change's description:
> > Mark GLSL reserved names as reserved in SkSL grammar.
> >
> > We now reject every reserved name in the ES2 docs as an unexpected
> > token, except for the rule that all names beginning with `gl_` are
> > reserved. (Unfortunately, sksl_frag bends the rules by directly
> > declaring a builtin variable named `gl_SecondaryFragColorEXT`.)
> >
> > Change-Id: I5dcb40b754720ca97fe3d80e2f9072beaa39fcdb
> > Bug: skia:11115
> > Reviewed-on: https://skia-review.googlesource.com/c/skia/+/454737
> > Auto-Submit: John Stiles <johnstiles@google.com>
> > Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
> > Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
>
> Bug: skia:11115
> Change-Id: Ica56f48dc76ef1e52780acaf59b8ad9143637637
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/454860
> Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
> Commit-Queue: Ethan Nicholas <ethannicholas@google.com>

Bug: skia:11115
Change-Id: I012b8d4e03be7f9c888c26d912552412529b4fb6
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/455159
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
83 files changed