* There's not a good accepted terminology for this kind of event, and for
historical reasons 'drawcall' has been the accepted term, even though
that can be quite confusing when a dispatch or a copy is a 'drawcall'.
* This is particularly highlighted by the event browser filters where
$draw() includes draws and dispatches, but $dispatch() only includes
dispatches, it's hard to intuitively understand why $draw() matches all
of these calls.
* As a result we've defined the term 'action' to cover these types of
events in the same way that we defined 'event' in the first place to
mean a single atomic API call.
* It's not particularly scalable and can be brittle to driver changes, and we
can use targeted specific pixel tests to check what we really want - to see if
the output has rendered correctly.
* Overlay tests still check files directly - this is a future refactor to
remove.
* This is better than testing by platform/platform version, because we can check
specifically for extensions and avoid running a test we know will fail because
extensions aren't supported.
baldurk