Ensure all Exodus element types have known topo-dims

[smason]

I've just been exploring some ExodusII files and I'm getting an exception:

  File "[...]meshio/src/meshio/_mesh.py", line 99, in __init__
    self.dim = topological_dimension[cell_type]
KeyError: 'tetra4'

It seems that there are a few element types, e.g. tetra4, that are known to the Exodus reader but don't have an entry in topological_dimension.

These changes adds a test that they all exist and fills in the missing entries.

AFAICT the order shouldn't matter so I've just shoved them in somewhere that looks nice – hope that's OK!

[smason]

looks related to #1296