[mlir][sparse] template the memory resident coordinate scheme storage

Rationale:
External file formats always store the values as doubles, so this was
hard coded in the memory resident COO scheme used to pass data into the
final sparse storage scheme during setup. However, with alternative methods
on the horizon of setting up these temporary COO schemes, it is time to
properly template this data structure.

Reviewed By: gussmith23

Differential Revision: https://reviews.llvm.org/D107001