[Impeller] Refactor all tessellation calls to use builder callback, rename.

[jonahwilliams]

Libtess gives all tessellation results at once. The old callback approach had to re-duplicate and push to vectors in order to give one point at a time. Previously, I introduced a callback that provided all vertices and indices at once avoiding that extra copy. We should update all callsites to use this, and rename it to just Tessellate.

Note that not all of our geometry can take advantage of this as strongly as the basic solid fill geometry. We still have an extra copy that is required to go from VBB into Host Buffer that can't be elimiated until we have AoS style bindingy-stuff available. But note, this is still fewer allocations than the point callback

[dnfield]

FWIW, if we do end up moving to the Lyon tessellator, it does offer an iterative per-vertex callback API, although I haven't dug into that to see whether it's just doing extra copies to achieve that.

That said, it shouldn't block this patch.