The presence of this was the main confusion point when I was trying to understand xrt_instance, because it's redundant now.
This does sadly increase the amount of per-target boilerplate (but only if you want to use a non-default instance). GUI and CLI targets now share the nearly-identical instance as the runtime, but with the compositor stubbed out.
Tested OpenXR target in both in-process and service mode, as well as testing gui and cli targets, and GUI debug mode in the OpenXR runtime target.
Fixes #83 (closed)