Adding nc_def_var_quantize()/nc_inq_var_quantize()

[edwardhartnett]

Adding nc_def_var_quantize()/nc_inq_var_quantize() as discussed in recent meeting.

This is a work in progress but I want to start running it through the CI to see if I am breaking anything. ;-)

Fixes #1548

[DennisHeimbigner]

I eventually came to the conclusion that the nc_inq_var_all function was a mistake
because it gets too cumbersome as parameters are added (like here).
We should consider adding an inq_var_quantize function to the dispatch table
instead of extending inq_var_all.