Removed static vector for thread safety. Accessing the original mesh ID
can now be done by `originalID[meshID]`, where `originalID` is a field
of `MeshRelation`. Note that `meshID` will not be updated when a
manifold is cloned. Instead, it is only used to identify triangles
coming from different manifolds when doing boolean operations/compose.

Disabled most of the importer/exporter formats by default, for faster
development and CI.

Note that you may need to CMakeCache.txt for this to take effect, as the
options might be cached.

... at the expense of the internal code becoming a bit less intuitive.
The meshID in the internal API is purely internal, usually starting from
0, which is used for differentiating between triangles coming from
different meshes. originalID can map this internal meshID to the
external meshID, and such mapping is automatically done when calling
`GetMeshRelation`, so users don't have to care about this mapping.

As a bonus, we don't need to deal with atomics when manipulating meshIDs
internally: we can use whatever IDs we want as long as the mapping is
preserved and distinct for triangles coming from different meshes.
I also made the meshID modification code run in the device, which should
be faster for larger meshes.