WebGPURenderer: Added double-side transmission 1/2

[sunag]

Related issue: #27880

Description

Adds an individual viewport texture to the back side of the objects. For many refraction objects in the scene with DoubleSide with transmission will need to modify the RenderList this may impact the performance a bit, which is why I am leaving it for another PR.

webgpu_materials_transmission

old	now

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	692.71 171.44	692.71 171.44	+0 B +0 B
WebGPU	818.16 220.56	818.2 220.58	+36 B +21 B
WebGPU Nodes	817.67 220.43	817.71 220.45	+36 B +18 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	464.93 112.2	464.93 112.2	+0 B +0 B
WebGPU	539.13 145.56	539.17 145.6	+36 B +32 B
WebGPU Nodes	495.16 135.43	495.16 135.43	+0 B +0 B