Feat/ogc3dtiles style pre sky

[ymoisan]

Note: This branch is based on master prior to the sky/atmosphere rendering merge (66a44d4), which introduced a camera/zoom regression I encountered. The changes in this PR are independent of that feature and should rebase cleanly once the regression is addressed.

Also, you will see in commit messages that code is generated by AI. however, I have made sure I understand the code and I have deliberately kept the code edits limited in scope to ease the work of reviewers.

PR message generated by AI; lightly modified by me

Description

Add per-feature styling capability to OGC3DTilesLayer, enabling color assignment by feature type (e.g. Building, SolitaryVegetationObject). The original intent was to provide interactive visual rendering for 3DTiles 1.1 but 3D Tiles 1.0 behavior should be preserved.

New functionality in OGC3DTilesLayer:

• Detect feature IDs from _FEATURE_ID_0 (3D Tiles 1.1) with _batchid (1.0) fallback
• Handle both indexed and non-indexed geometries when building feature groups
• Populate per-feature metadata from EXT_structural_metadata property tables into C3DTFeature.userData
• Support dynamic style application and removal via layer.style setter, with material caching
• Cache and restore original materials when style is toggled off
• Clean up tile features on dispose-model events

Bug fix in optimizeGeometryGroups (ThreeUtils.js):

• Only merge geometry groups that are contiguous in vertex space. Previously, groups sharing a materialIndex were merged unconditionally, which produced wrong vertex ranges when features of the same type interleave in the buffer (e.g. Building, Vegetation, Building).

Tests:

• 7 new unit tests covering feature init (1.1 + 1.0 fallback), indexed geometry, style apply, style restore, cleanup, and picking

Examples:

• New 3DTiles-11-styling.html: interactive per-type color picker for any tileset URL
• Updated OGC3DTilesHelper.js

Motivation and Context

There was no built-in way to style individual features in OGC3DTilesLayer by semantic type. Users working with CityGML-derived 3D Tiles (Buildings, Vegetation, etc.) had no API to assign colors per feature category.

This change brings OGC3DTilesLayer closer to the per-feature styling capabilities already present in the vector layer pipeline, and makes the 3D Tiles 1.1 EXT_structural_metadata / EXT_mesh_features extensions usable for styling.

Tested on Chrome 134 / Windows 11 (WSL2) with 3D Tiles 1.1 tilesets containing EXT_structural_metadata.

Screenshots

screenshot of 3DTiles-11-styling.html showing color pickers and styled features.