Tested versions

Every Godot version that launches the XR server triggers the XRServer to do expensive work, even if there are not XR interfaces available, burning CPU.

This is part of my investigation of why Godot was missing update frames on MacOS, despite doing nothing: #116845 (comment)

XRServer is not really my domain of expertise, but I would think that we should not really run any XR steps if there are no XR devices active:

this is called from Main iteration:

XRServer::get_singleton()->_process();

Measured in Rocket Chat thread as consuming 3% of CPU when idling: https://chat.godotengine.org/channel/apple?msg=zyz8Ey4X4qMmGM4xG

System information

Any platforms.

Issue description

CPU being burned.

Steps to reproduce

Start Godot with any empty project, sit idling, and run a profiler, you will see XRServer consuming plenty of CPU.

Minimal reproduction project (MRP)

Any empty project will do.