Don't allow packed integer types in glVertexAttribIPointer. They are only allowed in the glVertexAttribPointer call. BUG=angleproject:1101 Change-Id: I85aae9e35b45e8b1296244756091271d01dd1533 Reviewed-on: https://chromium-review.googlesource.com/376719 Reviewed-by: Corentin Wallez <cwallez@chromium.org> Commit-Queue: Geoff Lang <geofflang@chromium.org>