fix(types): `mapValues` index signature handling

[aleclarson]

[!TIP] The owner of this PR can publish a preview release by commenting /publish in this PR. Afterwards, anyone can try it out by running pnpm add radashi@pr<PR_NUMBER>.

Summary

mapValues was incorrectly handling index signatures at the type level:

// BEFORE
const object = mapValues({} as { [key: string]: number }, x => String(x))
//    ^? { [key: string]: string; [key: number]: string }

// AFTER
const object = mapValues({} as { [key: string]: number }, x => String(x))
//    ^? { [key: string]: string }

For any code change,

• [ ] Related documentation has been updated, if needed
• [x] Related tests have been added or updated, if needed
• [ ] Related benchmarks have been added or updated, if needed

Does this PR introduce a breaking change?

No

[aleclarson]

Also fixed handling of optional properties when exactOptionalPropertyTypes is true in your tsconfig.

For example, if the mapped object is of type { a?: number }, the mapping function will now receive a number instead of number | undefined.

[radashi-bot]

A stable release 12.2.1 has been published to NPM. :rocket:

To install:

pnpm add radashi@12.2.1