Allow record/map to transform type with optional properties

[baoshan]

The current implementation of record/map refuses to map a type with optional properties:

import * as R from "./record.ts";
type Foo = { bar: number; baz?: number };
const foo: Foo = { bar: 1 };
R.map((n: number) => n + 1)(foo);
                            ^^^

Because:

Argument of type 'Foo' is not assignable to parameter of type '{ bar: number; baz: number; }'.
  Property 'baz' is optional in type 'Foo' but required in type '{ bar: number; baz: number; }'

This PR allows such usage.

[baoshan]

Any chance this PR could have a review? Thanks.

[pixeleet]

@baoshan Thank you for your contribution!
Apologies for the non-timely review, we're in the cucumber season.

There's one non-blocking nitpick that we should discuss with @baetheus, but otherwise, LGTM.

[pixeleet]

LGTM

pending 1 non-blocking discussion/nitpick.

[baoshan]

Thanks for the review.

Switched to fenced ts block for now. Feel free to let me know if you want some hands to port existing examples to any chosen style.

[baetheus]

This looks good, just needs another deno fmt and I'll merge it right in.