Add fredemmott vendorID

[fredemmott]

Original discussion: https://github.com/KhronosGroup/OpenXR-SDK-Source/pull/319#issuecomment-1192688457

Software that will use this vendor id: https://github.com/fredemmott/OpenKneeboard/ - currently uses XR_APILAYER_NOVENDOR_OpenKneeboard.

Spec notes that vendor IDs should be reserved, and can be used for API layers - and, if you have a vendor ID, it should be used for all your API layers. However, it's unclear if it's fine to publish an API layer without an assigned vendor ID:

This usually takes the form of:

An OpenXR API layer prefix string: "XRAPILAYER"

The name of the vendor developing the API layer: e.g. "LUNARG_"

A short descriptive name of the API layer: e.g. "test"

If it is intended that api layers 'should' or 'must' register vendors, please approve this pull request, so I can use it in my software.

If this is not intended, perhaps the documentation should encourage the use of NOVENDOR or similar? This is used by several other projects, e.g. OpenXR toolkit

[CLAassistant]

All committers have signed the CLA.

[rpavlik]

Thanks for working with us on this!