Add render:includedPurposes option

[johnhaddon]

This allows the visibility of each individual USD purpose (default, render, proxy, guide) in interactive and batch renders to be controlled by a StandardOptions node. Similarly, a new menu in the Viewer provides the equivalent viewer-specific overrides, plus the option of falling back and using the settings from the scene.

What's missing here is the application of this option to the contents of Capsules when they're rendered. This is proving to be a bit fiddly, so I'd like to get the basics reviewed and merged first so that we can focus on just the Capsule details in a followup PR.

[murraystevenson]

This all seems to behave quite nicely. A couple of minor UI suggestions, but otherwise looks good.

I do wonder a bit at the practicality of being able to disable the "Default" purpose, seeing as that would typically remove all lights and cameras, but the option does seem worth including for completeness.

[johnhaddon]

This all seems to behave quite nicely. A couple of minor UI suggestions, but otherwise looks good.

Thanks for the review and the UI suggestions - I've pushed a fixup to address them.

I do wonder a bit at the practicality of being able to disable the "Default" purpose

Yeah, I did wonder a bit about that - maybe one potential use is to turn it off so you can use the Viewer to find all your "Proxy" objects? I've added a comment to the tooltip mentioning that maybe you probably don't want to turn it off other than for debugging.

[murraystevenson]

LGTM 👍 Thanks for those updates!