In the special case where you are loading the point coordinates for a
structured grid in a point to cell map (an important use case), create a
VecRectilinearPointCoordinates rather than build a Vec of the values.
This will activate the cell specalizations in previous commits.
These changes also added some flat-to-logical index conversion and vice
versa in ConnectivityStructuredInternals. This change also fixed a bug
in getting cells attached to points in 2D grids. (Actually, technically
someone else fixed it and checked it in first. The changes were merged
during a rebase.)
I also added a specalization to Vec for 1D that implicitly converts
between the 1D Vec and the component. This can be convenient when
templating on the Vec length.