can we make XRDepthStateInit optional?

[cabanier]

The depth sensing spec states that [XRDepthStateInit](XRDepthStateInit](https://immersive-web.github.io/depth-sensing/#dictdef-xrdepthstateinit) is required; even when the user doesn't set any values.
Can we make it optional instead?

Quest browser has it as optional and this is causing issues in three.js

/agenda can we make XRDepthStateInit optional?

[alcooper91]

Worth a mention that the samples don't appear to be supplying the XRDepthStateInit which is causing issues for Chrome at the moment since we do require it, so if we decide not to relax this, there's an AI to update the samples: https://immersive-web.github.io/webxr-samples/proposals/phone-ar-depth.html

[alcooper91]

Note that I'm also not sure about:

even when the user doesn't set any values

based on the algorithm here that essentially requires the returned usage/format to be contained in the array, so if the arrays are empty, no depth sensing session should be started:
https://immersive-web.github.io/depth-sensing/#find-supported-configuration-combination