WebGPURenderer: Rename PostProcessing to RenderPipeline

[sunag]

Related issue: #32535 (comment)

Description

Some processes we do in PostProcessing are not necessarily Post-Processing, and this ends up generating confusion, especially when used with the Inspector. I think the name Render Pipeline is quite clarifying in relation to the process as suggested by @Mugen87.

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	355.82 84.56	355.82 84.56	+0 B +0 B
WebGPU	621.5 172.57	621.71 172.64	+209 B +69 B
WebGPU Nodes	620.1 172.33	620.31 172.4	+209 B +68 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	488.06 119.45	488.06 119.45	+0 B +0 B
WebGPU	691.97 187.85	691.97 187.85	+0 B +0 B
WebGPU Nodes	641.77 175.02	641.77 175.02	+0 B +0 B