TSL: Introduce screenUV, screenSize, screenCoordinate and viewport revision

[sunag]

Related issue: Closes #29162

Description

viewportSize, viewportCoordinate, viewportUV, followed the logic related to viewport, while screenUV, screenSize and screenCoordinate followed the logic used previously and screen* considering the framebuffer.

Screen

Node	Description
screenUV	unitless in [ 0, 1 ] - normalized screen coordinates
screenSize	physical pixel units - framebuffer width,height resolution.
screenCoordinate	physical pixel units - framebuffer current x,y pixel position.

Viewport

Node	Description
viewportUV	unitless in [ 0, 1 ] - normalized viewport coordinates
viewport	physical pixel units - viewport rectangle x,y,width,height
viewportSize	physical pixel units - viewport width,height resolution.
viewportCoordinate	physical pixel units - viewport current x,y pixel position.

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	685.18 169.62	685.18 169.62	+0 B +0 B
WebGPU	825.96 221.44	826.2 221.55	+241 B +113 B
WebGPU Nodes	825.54 221.34	825.78 221.46	+241 B +118 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	461.96 111.46	461.96 111.46	+0 B +0 B
WebGPU	525.27 141.52	525.3 141.56	+25 B +36 B
WebGPU Nodes	481.93 131.34	481.95 131.37	+25 B +28 B

[WestLangley]

viewport | physical pixel units - viewport rectangle x, y, width, height
viewportSize | physical pixel units - viewport width, height resolution.

renderer.viewport is in logical pixel units. The viewport coordinates define the affine transformation from NDC coordinates to window coordinates.

I think it would be odd if viewport was in physical units and scaled by pixel ratio. A viewport knows nothing about pixel ratio.

[sunag]

The viewport must represent the entire hierarchy that follows. It would be strange and confusing for the user if viewport was logical pixel units and the rest were not. Just as renderer.getSize() is logical pixel units and viewportSize and screenSize are physical pixel units, for shaders we must have physical pixel units as default.