Support complex multi-mesh geometries

[gouldingken]

This mesh is not rendering correctly in r3f-speckle, but renders fine in the Speckle Viewer. It appears to be a low-level issue with how triangles are being represented - almost like a triangle gets skipped or something because some render fine while others render with holes where there should be triangles and triangles where there should be none.

https://sasaki.speckle.xyz/streams/25a13f78fa/commits/e9a486f2f4

Local test link:
http://localhost:5174/?streamId=25a13f78fa&commitObjectId=9d32e7ce12b714d3b803e45c08202dd3

[gouldingken]

Some reworking of this file since we copied it, but nothing that seems to affect triangulation of meshes:
https://github.com/specklesystems/speckle-server/blob/67b778b9269b25c930ef7c950d6c637e99d4470a/packages/viewer/src/modules/loaders/Speckle/SpeckleGeometryConverter.ts#L4

[gouldingken]

Breaking the problematic mesh into multiple simpler meshes confirms 2 things: it is not an issue with the meshes themselves, nor is it a problem with split meshes (since I kept some split meshes within the file - as highlighted in this image).

Split version (works): http://localhost:5174/?streamId=25a13f78fa&commitObjectId=2905c173d69076dc478cbe1111baecdd
Original version (broken): http://localhost:5174/?streamId=25a13f78fa&commitObjectId=9d32e7ce12b714d3b803e45c08202dd3