Replace glTF model implementation

[ptrgags]

Fixes #10346
Fixes #10416
Fixes #10379
Fixes #9303
Fixes #7062
Fixes #6299
Fixes #2387

This PR replaces CesiumJS's glTF model implementation. the old Model was removed, and ModelExperimental was renamed to Model as a drop-in replacement. The new architecture is a lot more decoupled, and it made it easier to implement features such as 3D Tiles Next metadata and CustomShader

This PR merges the staging branch replace-model into main. It includes changes from the following PRs:

• Throw RuntimeError for glTF 1.0 and unsupported extensions in ModelExperimental #10595
• Ensure spec parity between Model and ModelExperimental #10600
• Make ModelExperimental handle classification #10623
• Rename peripheral model classes #10639
• Remove ability to toggle classificationType at runtime #10643
• Update Model3DTileContent specs to have parity with 3D Tiles 1.0 formats #10633
• Remove old b3dm/i3dm/pnts content classes #10635
• Remove Model and rename ModelExperimental -> Model #10637
• Remove unused glTF models from Specs/Data #10642
• Fix development sandcastles #10646
• Clean up JSDoc for Model classes #10647

To Do:

• Update CHANGES.md with an announcement
• Test Sandcastles again
• Sweep through and see if we need to remove @experimental anywhere
• Add changes from Convert glTF 1.0 techniques to PBR materials by default gltf-pipeline#619 so we can have (limited) support for glTF 1.0 and KHR_techniques_webgl Will be done separately

[cesium-concierge]

Thanks for the pull request @ptrgags!

• ✔️ Signed CLA found.
• ❔ Unit tests were not updated.
  • Make sure you've updated tests to reflect your changes, added tests for any new code, and ran the code coverage tool.

Reviewers, don't forget to make sure that:

• Cesium Viewer works.
• Works in 2D/CV.

[lilleyse]

Does this implicitly close #10416 as well?

[ptrgags]

@lilleyse yes, it closes that issue as well as #10379. Possibly others too

[j9liu]

We should close the roadmap issue once this is merged: #10346
This could also close:

• Model mutates the gltf object parameter #9303
• Expose an interface to ModelInstanceCollection #7062 (ModelInstanceCollection no longer exists)
• Support gltf 2.0 POINTS #6299
• Change the material of a primitive in a ModelMesh #2387 (ModelMesh no longer exists)

[ptrgags]

@j9liu I updated the description so this PR closes those issues.

[j9liu]

@ptrgags @lilleyse merging now!