Refactor GraphicsProvider and add APIs for creating Seequent EVO tilesets

[eringram]

This PR adds a new concept of TilesetCreators and UrlProviders:

• The UrlProviders/ directory contains files with functions that call external services such as the mesh export service and Seequent EVO visualization service to retrieve urls to 3D tilesets
• The TilesetCreators/ directory contains files with functions that create/initialize tilesets using these urls

A pair of new files in these directories are GeoscienceUrlProvider.ts and GeoscienceTileset.ts. GeoscienceUrlProvider.ts contains getGeoscienceTilesetUrl which retrieves a url to a 3D Tiles tileset.json from Seequent, as described above. GeoscienceTileset.ts contains createGeoscienceTileset which uses that url to create and attach a reality model using Viewport.displayStyle.attachRealityModel. These APIs are marked as @alpha because they are experimental in collaboration with Seequent.

Used to be #6904. This is a copy of that branch with the display test app changes removed.

[pmconne]

singleton class

Why?

[danieliborra]

singleton class

Why?

Good point, we can make the functions static so we won't need a singleton.

The idea of the class is to centralise the access and generation of 3d tilesets.

[andremig-bentley]

Why?

Good point, we can make the functions static so we won't need a singleton.

The class has been changed to have only static methods, and the singleton has been removed.

[mergify[bot]]

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