WebGLBackend: Cache WebGL buffer when updating UBOs.

[Mugen87]

Fixed #31679.

Description

The PR fixes an issue where WebGL buffers were created over and over again for UBO updates.

The GL buffer is directly coupled to the buffer of THREE.UniformBuffer which is fixed sized. So creating the GL buffer for a UBO once and then caching it should be safe.

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	338.91 79.1	338.91 79.1	+0 B +0 B
WebGPU	575.57 158.81	575.75 158.85	+173 B +43 B
WebGPU Nodes	574.18 158.56	574.35 158.61	+173 B +44 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	470.7 113.91	470.7 113.91	+0 B +0 B
WebGPU	646.63 174.87	646.8 174.91	+173 B +41 B
WebGPU Nodes	600.8 164.05	600.98 164.09	+173 B +40 B

[Mugen87]

The code also distincts now between buffer update and creation. gl.bufferData() is only used for creation, gl.bufferSubData() for the update. In this way, we update UBOs in the same manner as attribute buffers.

[Mugen87]

The set() calls are changed to avoid inline object creation via {}.