Picking an initial OpenXR version

I'd love to have a way to more intelligently pick an OpenXR version, or version range! Currently, the only way to discover an OpenXR version is to provide a very specific version to `xrCreateInstance`, and check for `XR_ERROR_API_VERSION_UNSUPPORTED`.

This results in code that explicitly must check against every supported version using `xrCreateInstance`, which is not too burdensome yet, but becomes confusing when considering 'patch' versions, and burdensome when considering OpenXR 5-10 years in the future.

I'd also add that I've seen the documentation recommends calling `xrCreateInstance` with `XR_CURRENT_API_VERSION`. This seems fairly reasonable, but when using the latest version of the OpenXR Loader (1.1.36) this crashes with `XR_ERROR_API_VERSION_UNSUPPORTED`, since (as of the moment of writing) no OpenXR Runtime supports 1.1 yet. This seems like a related element that has some room for improvement.

Review the existing documentation for xrCreateInstance and the XR_CURRENT_API_VERSION recommendation. Determine the intended behavior for discovering or selecting an OpenXR version or range before changing the relevant documentation; the issue names no file or test, and the desired API direction remains unresolved.

Written by the indexing model from the issue text.