Implement stroke tessellation with indirect draws

Adds a vertex shader that maps a variable-length triangle strip to a
stroke and its preceding join. Adds a new op that generates stroke
instances from a path, bins them by log2 triangle strip length (using
SIMD for the calculations), and renders them with indirect draws.

Bug: skia:10419
Change-Id: I6d52df02cffe97d14827c6d66136957f1859f53b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/339716
Commit-Queue: Chris Dalton <csmartdalton@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
12 files changed