WebGLRenderer: Correctly generate mipmaps for 3D & Array RenderTargets

[gkjohnson]

Fixed #29628

Description

This PR ensures that the correct target type is passed into "bindTexture" for array and 3d render targets.

I've tested this with my 3d tiles use case and it works but the downside is that it's extremely slow and causes noticeable stalls (sometimes for what feels like almost a second or more) since gl.generateMipmap will regenerate the mipmaps for the whole volume target when just a single layer has been rendered to. This is especially problematic when rendering multiple layers per frame since that means the mip chain for the whole 3d texture will be generated every render (in this case ~256x256x900px). So for my use case I'll need something a bit different. Jotting a few potential thoughts down - maybe others have some better ideas:

• Only regenerate the mipmap after all layers have been rendered for a single frame (probably still too expensive for this particular case but probably useful for other 3d render target use cases).
• Copy texture data to a 2d render target to generate mipmaps and then copy the whole mip change to the target layer (only works for array texture targets).

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	690.67 171.1	690.8 171.12	+137 B +20 B
WebGPU	816.43 220.08	816.43 220.08	+0 B +0 B
WebGPU Nodes	815.94 219.95	815.94 219.95	+0 B +0 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	463.31 111.89	463.45 111.9	+143 B +12 B
WebGPU	538.61 145.41	538.61 145.41	+0 B +0 B
WebGPU Nodes	494.73 135.28	494.73 135.28	+0 B +0 B