WebXRManager: Disable left eye layer for right eye camera and vice versa

[mrxz]

Related issue: #31434

Description

Since #29742, layers enabled on the camera are inherited by the XR cameras. In addition, the special layers (1 and 2) are enabled for the left and right camera respectively.

This PR changes the logic slightly so that it not only enables the eye layers, but explicitly disables the eye layer for the other eye. This way the left eye camera will never render with the right eye layer and vice versa. Before this change that could still happen when the camera had these layers enabled.

This contribution is funded by Fern Solutions

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	338.01 78.83	337.99 78.83	-12 B -2 B
WebGPU	557.92 154.36	557.92 154.36	+0 B +0 B
WebGPU Nodes	556.84 154.16	556.84 154.16	+0 B +0 B

🌳 Bundle size after tree-shaking

Minimal build including a renderer, camera, empty scene, and dependencies.

	Before	After	Diff
WebGL	469.26 113.53	469.25 113.53	-12 B -2 B
WebGPU	633.22 171.39	633.22 171.39	+0 B +0 B
WebGPU Nodes	588.35 160.71	588.35 160.71	+0 B +0 B

[Mugen87]

FYI: Added this change to XRManager (WebGPURenderer) as well: f614ed3