Add an isinf() polyfill for tessellation shaders

Tessellation uses infinity to flag conics, and also as a conic weight
that converts them into triangles. The es2 shading language doesn't
support infinity. This CL adds a "portable infinity" mode, where we
pretend inputs >= 2^126 are infinity. The rationale for doing this is
that those numbers are so large, they will overflow if we try to do any
bezier math with then anyway.

Bug: chromium:1220246
Change-Id: I3ad29ebb6fbbad5d23cfdba7a2717605009f8180
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/423697
Commit-Queue: Chris Dalton <csmartdalton@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
29 files changed