Implement OES_vertex_array_object.

Implement OES_vertex_array_object.

This extension works the same as OpenGL ES 3.0 vertex arrays, but requires
entry points with the OES suffix.

Change-Id: I82b92bbcec078f88becee6f3b37eb7e8256a1233
Reviewed-on: https://swiftshader-review.googlesource.com/18808
Tested-by: Krzysztof Kosiński <krzysio@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>