The redesigned code places the internal buffers and input elements for
instance point sprite emulation (FL9_3) at the start of the arrays,
instead of swapping with the first non-instanced element. This makes
the tracking logic of the caching somewhat cleaner.

This facilitates the work of implementing instancing-on-instancing for
FL9_3 conformance.

BUG=angleproject:1279

Change-Id: Ifb030816a313b1e8b916c57ef05915914443312a
Reviewed-on: https://chromium-review.googlesource.com/325090Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>