WebGPURenderer: extract common draw call logic from backends

[aardgoose]

Add a new method renderObject.getDrawParameters() to provide draw call parameters to the backend renderer.

Most of the logic is identical, apart from multidraw which has been left as-is. The separation of this from the current draw path will allow indirect drawing without duplicating this code again.

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	685.24 169.64	685.24 169.64	+0 B +0 B
WebGPU	826.2 221.55	826.35 221.59	+147 B +41 B
WebGPU Nodes	825.78 221.46	825.93 221.5	+147 B +41 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	462.02 111.48	462.02 111.48	+0 B +0 B
WebGPU	525.3 141.56	525.44 141.6	+147 B +49 B
WebGPU Nodes	481.95 131.37	482.1 131.42	+147 B +49 B