Move feather join tessellation to the draw shader

We need to flatten feathered curves in the tessellation shader, but this means the tangents won't be known until after the tessellation shader finishes. In order to work with this constraint, don't work out feather join stepping until the vertex portion of the draw shader. At this point, tessellation has finished flattening all the curves and the tangents are all known.

In the future, we should update all joins to work out their stepping in the draw stage. This would alleviate the need for the CPU to figure out and send join angles to the GPU.

Diffs=
07ffc16467 Move feather join tessellation to the draw shader (#9107)

Author: csmartdalton

.rive_head

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