feat(stdlib): List.Associative Submodule

[spotandjake]

This pr adds a List.Assocative submodule which contains functions for working with key-value pairs in lists.

let data = [
  ("name", "Alice"),
  ("name", "Bob"),
  ("age", "30"),
]
assert List.Associative.get("name", data) == Some("Alice")

Use case

This is similar to the associative list methods in ocaml https://ocaml.org/manual/5.2/api/List.html#1_Associationlists

I wasn't quite sure if we wanted this in the standard library or not but I think the pattern occurs enough with record information that it makes sense. A few examples being Map.toList, JSONObject.
Currently duplicates are ignored and the first item is always treated as the one your referring too.

Alternative proposal

An alternative proposal to this pr is we implement a new Collection module, where collections are of type abstract type Collection<key, value> = List<(key, value)> and then in that case we can handle the duplication semantics when you do List.toCollection, I think this might be overkill though.

[ospencer]

This PR is beautiful, but the spacing in your PR description is a crime.

[ospencer]

I love this but would like to see additional input from @alex-snezhko or @phated.

[alex-snezhko]

Yeah I'm totally in favor of this, I've basically had to implement this functionality myself several times so I think it makes sense to include in the stdlib

[alex-snezhko]

For cases where there are duplicate keys in the array what do you think about a getAll or something which would return a list of all matches. Could also do something similar for set and remove

[spotandjake]

What if we just had an all=false defaulted argument.

[alex-snezhko]

You can't really do that because the return type would change

[spotandjake]

That's fair enough, in that case I think we should have the getAll, removeAll and we might as well add setAll though I feel like that one isn't quite as useful.