Move GrTessellator::VertexAllocator to GrEagerVertexAllocator

Moves the interface up to Ganesh level and starts using it from other
locations.

Change-Id: I939d2b357d3ae8551976d0d71b877b72da403712
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/266063
Reviewed-by: Stephen White <senorblanco@chromium.org>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
9 files changed