Implement new builder syntax alongside old one

[smores56]

This PR implements the new style of the record builder syntax (using map2 functions) as described by @agu-z in this Zulip thread.

• Since the old syntax works differently from the new one, there's no way to automatically upgrade existing record builders, but at least for now, the old syntax is still supported. The old syntax has been renamed to "old-style record builders" in the code and in our error reporting to imply to users that the old version of record builders are out-of-date. We have freedom with this PR to decide at our leisure when to deprecate the old style.
• This PR only handles the implementation, I'm doing the documentation and website/tutorial updates in a separate PR to keep the size small.
• This does not support assigning _ to ignore record builder fields, that can be added after by updating the desugar.rs logic WRT handling malformed field names.

Here's an example of the syntax that works with this branch:

app [main] {
    pf: platform "https://github.com/roc-lang/basic-cli/releases/download/0.10.0/vNe6s9hWzoTZtFmNkvEICPErI9ptji_ySjicO6CkucY.tar.br",
}

import pf.Stdout
import pf.Task exposing [Task]

main =
    # ! desugaring works for the field values and the whole record
    multipleIn =
        { sequential <-
            a: Task.ok 123,
            b: Task.ok "abc",
            c: Task.ok [123],
            d: Task.ok ["abc"],
            e: Task.ok (Dict.single "a" "b"),
        }!

    Stdout.line! "For multiple tasks: $(Inspect.toStr multipleIn)"

sequential : Task a err, Task b err, (a, b -> c) -> Task c err
sequential = \firstTask, secondTask, mapper ->
    first = firstTask!
    second = secondTask!
    Task.ok (mapper first second)

Which prints

For multiple tasks: {a: 123, b: "abc", c: [123], d: ["abc"], e: {"a": "b"}}

[agu-z]

Good job! I left a few comments on potential improvements and some nitpicking.

I'm really looking forward to this 😄

[agu-z]

It'd be nice to add some "end-to-end" tests (maybe in cli?) that actually ran some record builders

[smores56]

I've added a few tests in the crates/cli/tests/cli folder that use the builder pattern, one using tasks, the other parsing args. Speaking of arg parsing, I've updated Weaver in this PR to use the new syntax, if anyone wants to see an example usage.

[agu-z]

Nice! Thanks for all the updates. I left some optional suggestions.

[agu-z]

This seems like a leftover comment

[agu-z]

I'd simplify this a bit. Using the word "mapper" might confuse people if they think it's a common term and they try to google it.

Suggested change

	Note: Record builders need a mapper function before the `<-` to combine
	fields together with.
	Note: Record builders need a function before the `<-` to combine fields.

Once we update the tutorial, I think we should include a link to the record builders section here.

[agu-z]

nit: Not using arena, you could just use map here.