List.length .isEmpty checks on Dict, Set and Array.toList (and more)

[morteako]

Simplifies uneccessary convertions from a Collection into List before a List.length / List.size, when you could just do
Collection.size or Collection.isEmpty

Mentioned before in comment here: #290 (comment)

Also adds one simplification for Array.length (Array.fromList list)

Simplifications:

Array

-- The following simplification also works for Array.toIndexedList
List.length (Array.toList array)
--> Array.length array

-- The following simplification also works for Array.toIndexedList
List.isEmpty (Array.toList array)
--> Array.isEmpty array

Array.length (Array.fromList list)
--> List.length list

Set

List.length (Set.toList set)
--> Set.size set

List.isEmpty (Set.toList set)
--> Set.isEmpty set

Dict

-- The following simplification also works for Dict.keys, Dict.values
List.length (Dict.toList dict)
--> Dict.size dict

-- The following simplification also works for Dict.keys, Dict.values
List.isEmpty (Dict.toList dict)
--> Dict.isEmpty dict

[lue-bird]

💙

[lue-bird]

If you want, add this to CHANGELOG.md under unreleased:

The rule now simplifies:
- `Array.length (Array.fromList list)` to `List.length list`
- `List.length (Array.toList array)` to `Array.length array` (same for `Array.toIndexedList`)
- `List.isEmpty (Array.toList array)` to `Array.isEmpty array` (same for `Array.toIndexedList`)
- `List.length (Set.toList set)` to `Set.size set`
- `List.isEmpty (Set.toList set)` to `Set.isEmpty set`
- `List.length (Dict.toList dict)` to `Dict.size dict` (same for `Dict.values` and `Dict.keys`)
- `List.isEmpty (Dict.toList dict)` to `ict.isEmpty dict` (same for `Dict.values` and `Dict.keys`)

[jfmengels]

This looks good to me, thank you @morteako 😊