Calculate join tessellation values in the vertex shader
Calculate join tessellation values in the vertex shader

Each patch has one join and one set of stroke parameters, so the
vertex shader is the correct place to do it. This is also an important
cleanup that will allow us to create "dynamic" stroking parameters and
batch together strokes with different join types or stroke widths.

Bug: chromium:1172543
Bug: skia:10419
Change-Id: Icef0c20858fba6c18685006550dc75246710cd35
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/368043
Reviewed-by: Brian Salomon <61fabaaf0876044aeedfd8e351e485c028d69e7b@google.com>
Commit-Queue: Chris Dalton <ef7fc3a08ada7d31f16e9a18b5f3c728256e041e@google.com>

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