smyrna: duplicate names when creating new grid columns

smyrna: duplicate names when creating new grid columns

This is a step towards solving a memory leak. Note that this involved rewriting
some string comparisons because the originating pointer is no longer stored in
the column’s `name`. It is not clear to me how the previous code was valid
because, e.g., it was comparing by pointer to the `Visible` constant to detect
when a column was called “Visible”. That is, nothing actually assigns a column
name to the address of `Visible`.

Gitlab: #2299