A new enum is being created that contains command types, which are then
passed to each dirty object when they are synced. This allows the
syncState() methods to perform special handling for each command type.

This change is in preparation for optimizing resolving multisample
images with glBlit, since the render pass needs to be updated before
it's ended.

Bug: angleproject:4753
Change-Id: I77701f79418d35cff689e864c8a8b47b6fca0255
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2327335
Commit-Queue: Tim Van Patten <timvp@google.com>
Reviewed-by: Charlie Lao <cclao@google.com>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>