sort(List) MonomialOrder option

Sorting a list while specifying MonomialOrder=>Descending still sorts the contents in ascending order. For sorting matrices, it seems to work fine.

Example:

```
i1 : sort(flatten entries basis(0,2,QQ[x,y]), MonomialOrder=>Descending)

2 2
o1 = {1, y, x, y , x*y, x }

o1 : List

i2 : sort(basis(0,2,QQ[x,y]), MonomialOrder=>Descending)

o2 = | x2 xy y2 x y 1 |

1 6
o2 : Matrix (QQ[x, y]) <--- (QQ[x, y])
```

Start by running the reported sort(List) examples with MonomialOrder=>Descending, comparing the flattened list with the matrix result. Trace the sort(List) handling of MonomialOrder and verify that the list is returned in descending monomial order while matrix sorting remains unchanged.

Written by the indexing model from the issue text.