WebGLRenderer: Support MRT for 2d array textures

[mrxz]

Related issue: #30151

Description

Adds support for 2d array textures and 3d textures when using multiple render targets. The setupRenderTarget method in WebGLTextures made the assumption that for multipleRenderTargets (textures.length > 1) the individual textures would be TEXTURE_2D. This is changed to also handle TEXTURE_2D_ARRAY and TEXTURE_3D.

The layer passed to setRenderTarget is used for all targets. Binding different layers as touched upon in #30151 is not part of this PR.

This contribution is funded by Fern Solutions

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	337.92 78.83	338.12 78.86	+200 B +27 B
WebGPU	560.22 155.1	560.22 155.1	+0 B +0 B
WebGPU Nodes	559.14 154.89	559.14 154.89	+0 B +0 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	469.19 113.49	469.39 113.53	+200 B +33 B
WebGPU	635.38 172.03	635.38 172.03	+0 B +0 B
WebGPU Nodes	590.03 161.27	590.03 161.27	+0 B +0 B