Support resolving `.ts` files from `.js` extensions

[benjamind]

Modern NodeNext resolve strategies, and Typescript team itself historically, require that imports end with .js extension.

The plugin right now simply appends extensions to try, rather than changing extensions. So if you have a TS project and have an import of the form:

import { Foo } from './foo.js';

The file to resolve may actually be called foo.ts on disk, and hence the current plugin resolve strategy won't find it.