Update GrInnerFanTriangulator to use an existing SkArenaAlloc

For the tessellation op this allows it to use either the record-time
or flush-time allocator instead of making its own.

Bug: skia:10419
Change-Id: Ida13283feffda1976bd8fd221d5be0013a5de990
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/356516
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
8 files changed