Line2NodeMaterial: Align wide lines with WebGLRenderer version.

[Mugen87]

Related issue:

Description

As suggested in #32229 (comment), the PR makes sure the wide line implementation for WebGPURenderer uses CSS pixel units to ensure consistent line widths across devices. For this, the DPR must be factored out of the viewport.

With this PR, the wide line demos now render with equal width for WebGPURenderer and WebGLRenderer.

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	356.24 86.48	356.24 86.48	+0 B +0 B
WebGPU	610.49 171.27	610.5 171.28	+8 B +7 B
WebGPU Nodes	609.1 171.01	609.1 171.02	+8 B +8 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	488.02 121.25	488.02 121.25	+0 B +0 B
WebGPU	679.43 186.52	679.43 186.52	+0 B +0 B
WebGPU Nodes	621.15 169.7	621.15 169.7	+0 B +0 B