WebGLRenderer: Add support for WEBGL_render_shared_exponent.

[Mugen87]

Related issue: #27971

Description

The renderer now supports WEBGL_render_shared_exponent so the internal format RGB9_E5 can be used. The idea is to pack float data via gl.UNSIGNED_INT_5_9_9_9_REV into Uint32Array. We have to add THREE.RGBFormat back for that.

A minimal data texture setup with THREE.RGBFormat and the new THREE.UnsignedInt5999Type type looks like so:

const data = new Uint32Array( 4 * 4 );
	
const texture = new THREE.DataTexture( data, 4, 4 );
texture.format = THREE.RGBFormat;
texture.type = THREE.UnsignedInt5999Type;

/cc @elalish

Related: https://stackoverflow.com/q/55692758/5250847

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

Filesize dev	Filesize PR	Diff
671 kB (166.3 kB)	671.2 kB (166.4 kB)	+222 B

🌳 Bundle size after tree-shaking

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

Filesize dev	Filesize PR	Diff
450.9 kB (108.9 kB)	451.1 kB (109 kB)	+163 B

[Mugen87]

As mentioned in #27971 (comment), I think we can try the computations of https://registry.khronos.org/OpenGL/extensions/EXT/EXT_texture_shared_exponent.txt to figure out a helper method that converts three RGB floats (FP32) into a single packed Uint32.

[Mugen87]

The last two commits also add support to WebGPURenderer for both WebGPU and WebGL backend.

[elalish]

@lexaknyazev - thanks for pointing me to WEBGL_render_shared_exponent; I mentioned it to Three.js and they've already adopted it.