Line2NodeMaterial: Fix broken dash.

[Mugen87]

Fixed #28884.

Description

This PR fixes the broken dash by moving some of the computations to the vertex shader where they actually belong to. Besides, it makes sure dashOffset can be configured for LineDashedNodeMaterial.

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	692.22 171.45	692.22 171.45	+0 B +0 B
WebGPU	825.22 222.85	825.32 222.86	+106 B +16 B
WebGPU Nodes	824.33 222.64	824.44 222.66	+106 B +16 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	464.58 112.26	464.58 112.26	+0 B +0 B
WebGPU	545.43 147.71	545.49 147.75	+61 B +36 B
WebGPU Nodes	501.37 137.44	501.37 137.44	+0 B +0 B