Merged back RecordableGraphResource into CommandGraphResource.  Queries
didn't really need to be a resource, as they always inserted separate
single-command nodes in the graph.  The CommandGraph class is augmented
with a few functions that generate such nodes.

This is in preparation for debug markers, as they too require such
nodes.

Bug: angleproject:2853
Change-Id: I5251a0e0fdd42ed1126921b4acc13687a14af9cd
Reviewed-on: https://chromium-review.googlesource.com/c/1422549
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>