3d tiles renderer js migration

[mgermerie]

Description

Migrate towards 3DTilesRendererJS for 3D tiles. This PR is a draft from a branch initiated by @jailln on which all work related to 3D tiles migration should be merged before migration is complete and this PR can be merged.

Already implemented (don't hesitate to add what you implemented and was merged onto 3d-tiles-migration branch :

• [x] Create a new 3D tiles layer using 3dtilesrendererjs and deprecate C3DTilesLayer
• [x] Draco and KTX2 support
• [x] Cesium ion support
• [x] Google 3D tiles support
• [x] Gltf 1.0 support
• [x] CESIUM_RTC GLTF 1.0 extension support
• [x] itowns PointsMaterial support (ongoing)

Motivation and Context

2225

Remaining TODO

See the full list here