BatchedMesh: Consolidate internal geometry information

[gkjohnson]

Related issue: #29624, #29603

Description

Clean up for the BatchedMesh class to make things a little bit more clear and easier to manage:

• Consolidate the geometry data stored in _bounds, _reservedRanges, and _drawRanges into a common _geometryInfo member.
• Remove unnecessary comments
• Fixes BatchedMesh edge case: wrong frustum when perObjectFrustumCulled = false #29603

(removed the following changes to reduce noise in the change set, will re-add them in a followup)

• Remove some unnecessary global fields
• Rename "drawInfo" to "instanceInfo" for clarity
• - Expose information about instance count, unused vertex & index count so applications can make decisions about whether geometries can be added.

Once the class is finished and cleaned up I'll make an issue to discuss how we should move forward with the BatchedMesh implementation.

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	690.8 171.12	690.9 171.07	+93 B -51 B
WebGPU	816.46 220.09	816.55 220.03	+93 B -55 B
WebGPU Nodes	815.97 219.96	816.06 219.9	+93 B -56 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	463.45 111.9	463.45 111.9	+0 B +0 B
WebGPU	538.64 145.42	538.64 145.42	+0 B +0 B
WebGPU Nodes	494.75 135.28	494.75 135.28	+0 B +0 B