Reland "Rearrange SkSL pre-include modules to hide things"

This reverts commit 4cb5c5e1728933637ca9b8653ff95f876871dc9b, and fixes
the Chromium issue by declaring sign(x) in sksl_public.sksl.

Original description:

This makes numerous internal and GLSL types or intrinsics hidden from
public (runtime effect) SkSL. In particular:

- Only core numeric types are visible to all program types. GLSL types
  involving images, textures, and sampling are restricted to internal use.
- sk_Caps is no longer visible to runtime effects.
- The set of intrinsics available to runtime effects is now a separate,
  curated list in sksl_public.sksl. It exactly matches the GLSL ES 1.00
  spec order.
- The blend intrinsics are no longer visible, which also fixes a bug.
  These are nice, but we're not going to offer them yet - they involve
  enums, which creates complications.

Bug: skia:10680
Bug: skia:10709
Bug: skia:10913

Cq-Include-Trybots: luci.chromium.try:linux-chromeos-rel,linux-rel
Change-Id: I42deeeccd725a9fe18314d091ce253404e3572e2
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/332750
Commit-Queue: Brian Osman <brianosman@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
Auto-Submit: Brian Osman <brianosman@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
Reviewed-by: John Stiles <johnstiles@google.com>
10 files changed