Translated attributes are now stored in the VertexArray11 in a cache,
and only updated when dirty bits change. Currently dynamic attributes
must be re-translated every call, so these are stored in a list and
processed repeatedly.

This skips doing a lot of the VertexDataManager work for vertex
attributes that don't change between draw calls.

Current value attributes, which correspond to disabled attributes that
the program will pulls vertex data from, are owned by the Context, so
these need to be handled outside of the VertexArray11.

Further changes will be necessary to reduce the redundant work we do in
the InputLayoutCache. We shouldn't need to re-check the cache if
nothing relevant changed.

This give about a 23% performance improvement on the draw call
benchmark on my machine.

Re-land with a fix for the start vertex offset.

BUG=angleproject:1327

Change-Id: Ic23e48fb18ed7f29c1999914a2f799ac04aa03e9
Reviewed-on: https://chromium-review.googlesource.com/334225Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>