Create types package for loader-utils@3

[TheLarkInn]

@types/loader-utils only have support for loader-utils v1/v2. Since we have a new major version, I would like to just create the typings file for loader-utils@3 since there is significant type changes to LoaderContext for webpack 5.

[alexander-akait]

Yeah, feel free to send a PR

[TheLarkInn]

@alexander-akait is there any reason we couldn't just convert this package to using TypeScript. It's small enough and is probably a good test project if we wanted to convert others to TypeScript. I'm thinking about taking this route.