[GAML] Add `map_with`

[Vezonne]

Is your request related to a problem? Please describe.
In some cases, building a map dynamically can be tricky.

Describe the improvement you'd like
It might be useful if there was an operator map_with like list_with and matrix_with.

[AlexisDrogoul]

Fixed in #699. The proposed syntax uses a pair to generate the contents (a bit like as_map). E.g. map m <- 10 map_with (each::(each+1)); which returns [0::1, 1::2, ...]. substitution of each by another variable is of course possible; e.g. map m <- 10 map_with (i: i::(i+1));