Simplify stroke join definitions in tessellation shaders

All of a join's information can fit in a single float value:

    Negative => Round Join
    Zero     => Bevel Join
    Positive => Miter join, and the value is also the miter limit

Bug: chromium:1172543
Bug: skia:10419
Change-Id: I50bd822a735987cf21537164267d00e3f34badc5
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/369457
Commit-Queue: Chris Dalton <csmartdalton@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
1 file changed