Don't assume that an inputsourceschange event will be fired at the start of the session

Description of the problem

Currently, the three.js code setting up XR controllers only does this setup when an inputsourceschange event is fired. However, it is possible for a session to start with controllers already attached. My understanding is that Chrome will always fire inputsourceschange events at the beginning of the session, but I don’t think this is necessary according to the spec. Servo currently just starts off with the correct input sources, only spawning events when things change.

We should instead initialize the controller map when the session is created.

https://github.com/mrdoob/three.js/blob/fb29d21e65c2cb8a0bf8b797c0deefa5fe8c8cde/src/renderers/webxr/WebXRManager.js#L233

Three.js version

• Dev
• r113
• …

Browser

• All of them
• Chrome
• Firefox
• Internet Explorer

OS

• All of them
• Windows
• macOS
• Linux
• Android
• iOS

Hardware Requirements (graphics card, VR Device, …)

• VR Device

[Manishearth]

Yes.

[Mugen87]

Unnecessary due to upstream spec changes (immersive-web/webxr#961).

As far as I understand, this issue and the respective PR #18639 can be closed then, right? The tweaks to the specs ensure that inputsourceschange should be fired on start by WebXR implementations, correct?