BatchedMesh: Add optimize().

[gkjohnson]

Related issue: #29463, #28638

Description

Based on #29523 (must merge first)

Adds an "optimize" function to BatchedMesh that shifts geometry internally to overwrite the memory of unused / deleted geometry data. The method used here does not require any id mapping or indirection and just adds a new function.

cc @agargaro @Makio64 @Shakhriddin

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	687.47 170.27	688.13 170.5	+655 B +230 B
WebGPU	806.14 217.06	806.79 217.29	+655 B +236 B
WebGPU Nodes	805.64 216.92	806.3 217.16	+655 B +235 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	462.85 111.79	462.85 111.79	+0 B +0 B
WebGPU	535.59 144.55	535.59 144.55	+0 B +0 B
WebGPU Nodes	491.75 134.31	491.75 134.31	+0 B +0 B