Instead of splitting attributes into 'active enabled' and 'active
disabled', split them into static/dynamic/direct/current value, and
handle each group invidually. This also will allow the dirty bits
code to call in to the VertexDataManager separately for each type
of necessary vertex data translation, and skip it entirely for
direct buffer storage.

Should be a refactoring patch only.

BUG=angleproject:1327

Change-Id: I53cb5672054d99ae68e9aa2e5a3c046a002e360d
Reviewed-on: https://chromium-review.googlesource.com/330171Reviewed-by: Zhenyao Mo <zmo@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>