WebGPURenderer: Reduce memory churn when using chain maps.

[Mugen87]

Related issue: -

Description

While working at the docs, I've noticed WebGPURenderer allocates temporary array objects when using chain maps. Most of the methods using chain maps are executed at least once per frame. To keep the GC overhead to a minimum, we should avoid this kind of object creation whenever possible.

This PR ensures modules using a chain map manage their keys array in module scope. This pattern has already been adopted in RenderObjects and is now used globally. Besides, at the end of the chain map usage the array is truncated to a length of 0 otherwise it would keep references to objects like scenes or cameras. We do something similar in RenderList.finish() to ensure user created objects can actually GC collected. Setting the array length to 0 should still be the fastest way to clear an array in JavaScript.

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	339.44 79.06	339.44 79.06	+0 B +0 B
WebGPU	489.62 135.75	489.78 135.84	+165 B +92 B
WebGPU Nodes	489.08 135.64	489.25 135.73	+165 B +93 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	465.3 112.11	465.3 112.11	+0 B +0 B
WebGPU	559.12 151.27	559.28 151.36	+165 B +85 B
WebGPU Nodes	515.19 141.06	515.36 141.13	+165 B +77 B