PMREMGenerator: Add size and position options to fromScene().

[Mugen87]

Fixed #30071.

Description

The PR is an alternative implementation to #30334 and introduces a new options parameter to PMREMGenerator.fromScene() that allows to customize the size of the PMREM as well as the position of the internal cube camera.

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	336.12 78.22	336.28 78.27	+158 B +52 B
WebGPU	517.54 143.78	517.73 143.83	+186 B +57 B
WebGPU Nodes	517.01 143.66	517.2 143.72	+186 B +55 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	465.17 112.09	465.32 112.14	+159 B +46 B
WebGPU	589.44 159.86	589.63 159.95	+187 B +87 B
WebGPU Nodes	544.8 149.41	544.99 149.48	+187 B +70 B