TSL: Fix positionView sub-build

[sunag]

Fixes #32686

Description

This corrects the Clip Space implementation when using .vertexNode and reusing the positionView in the fragment stage.

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	355.36 84.47	355.36 84.47	+0 B +0 B
WebGPU	621.54 172.59	621.57 172.6	+31 B +10 B
WebGPU Nodes	620.15 172.35	620.18 172.36	+31 B +11 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	487.31 119.25	487.31 119.25	+0 B +0 B
WebGPU	692.53 187.85	692.57 187.86	+31 B +9 B
WebGPU Nodes	642.34 175.07	642.37 175.08	+31 B +10 B

[Mugen87]

Tested the changes with the reproduction test case and I can confirm the PR fixes the issue 🎉 .