Add support for foveation during additional render passes

[cabanier]

Proposal to foveate a user provided texture. I need to talk to the immersive group about adding this new API.

Without this feature:
Surface 2 | 3360x1760 | color 32bit, depth 24bit, stencil 0 bit, MSAA 4, Mode: 1 (HwBinning) | 63 384x256 bins ( 63 rendered) | 1.38 ms | 128 stages : Binning : 0.194ms Render : 0.727ms StoreColor : 0.133ms Blit : 0.004ms

With this feature:
Surface 8 | 3360x1760 | color 32bit, depth 24bit, stencil 0 bit, MSAA 4, Mode: 1 (HwBinning) | 72 288x320 bins ( 38 rendered) | 1.26 ms | 78 stages : Binning : 0.161ms Render : 0.514ms StoreColor : 0.31ms Blit : 0.004ms

Don't pay too much attention to the timings as they depend on the content that is on the screen. The important part is that there are fewer rendered "bins" since they're bigger in the foveated areas.

[cabanier]

WIP. Not for merging yet

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	336.27 78.29	336.27 78.29	+0 B +0 B
WebGPU	517.08 143.61	517.48 143.71	+402 B +102 B
WebGPU Nodes	516.54 143.5	516.95 143.6	+402 B +103 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	465.25 112.13	465.25 112.13	+0 B +0 B
WebGPU	589.09 159.7	589.49 159.8	+402 B +103 B
WebGPU Nodes	544.45 149.25	544.85 149.36	+402 B +105 B