Use switch statements based on the format type enum, instead of
a map from the old VertexFormat structure to the info payload.
This saves on lookup and initialization time.

BUG=angleproject:959

Change-Id: I6d1bf282c88f67272ca067cb64bc71e77824a12e
Reviewed-on: https://chromium-review.googlesource.com/277290Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>