Reland "Move last join control point storage into PatchWriter"

This reverts commit 35e34d8db246398830566d83ea4140efec214dac.

Reason for revert: circles were corrupting join point; fix in PS1->PS2

Original change's description:
> Revert "Move last join control point storage into PatchWriter"
>
> This reverts commit 1f1270f8accfee1b1de1aa9336a70249df2f9b63.
>
> Reason for revert: unexpected gold diffs crept in after PS2...
>
> Original change's description:
> > Move last join control point storage into PatchWriter
> >
> > Change-Id: I916c23778e04911ea122720b8e48850caab4df64
> > Reviewed-on: https://skia-review.googlesource.com/c/skia/+/501437
> > Reviewed-by: John Stiles <johnstiles@google.com>
> > Commit-Queue: Michael Ludwig <michaelludwig@google.com>
>
> Change-Id: I143a6a16e2ecef735f5c67995e92d315ab463121
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/502697
> Auto-Submit: Michael Ludwig <michaelludwig@google.com>
> Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
> Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>

Change-Id: I4bd7479da9d5bcb15a3ce6cef25fdda97aa25d3a
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/502785
Auto-Submit: Michael Ludwig <michaelludwig@google.com>
Reviewed-by: Christopher Dalton <csmartdalton@google.com>
Commit-Queue: Michael Ludwig <michaelludwig@google.com>