Add list sort builtins using a new ordering API

[jrrrp]

Following the discussion in Zulip^1 this PR

• Converts LT/EQ/GT ordering tags to FirstBeforeSecond, Equivalent, SecondBeforeFirst to denote which of the two arguments in the comparison comes before the other. This decouples ordering from "less than" and by extension from the operators <, > etc.
• When a default sort is desirable, modules can implement t.default_cmp : t, t -> [FirstBeforeSecond, Equivalent, SecondBeforeFirst]
• Integers and tuples are two such primitives where it may make sense to have a default ordering, unlike strings.

Testing

• Updated existing tests referencing List.sort_with

Todo

• Remaining list builtins (sort_by, reverse) and snapshot tests. They will eventually be re-implemented in Zig but I figured it could be solidified in Roc first.

---

Before I finish I thought I'd check that the naming is still ok:

List.sort(list, comparison_func)
List.sort_with_default(list)
item.default_cmp(other) # Returns one of [FirstBeforeSecond, Equivalent, SecondBeforeFirst]
List.sort_by(list, mapper_fn)

# Reverse:
List.sort_rev(list, comparison_func)
List.sort_with_default_rev(list)
List.sort_by_rev(list, mapper_fn)

In particular, sort_with_default_rev is quite verbose, and if you want to define a comparison function inline, it looks like this:

expect [3, 1, 2].sort(|a, b| if a < b FirstBeforeSecond else if a > b SecondBeforeFirst else Equivalent) == [1, 2, 3]

[1] https://roc.zulipchat.com/#narrow/channel/304641-ideas/topic/Sorting.20tuples.3F/with/606333839
https://roc.zulipchat.com/#narrow/channel/304641-ideas/topic/List.20sort.20builtins/with/605016649