sub-path imports on library code

[NullVoxPopuli]

rollup/plugins#1077

Example:

import { nodeResolve } from '@rollup/plugin-node-resolve';

export default {
	plugins: [
		nodeResolve({
			resolveOnly: module => module.startsWith('#'),
		}),
	],
};

we want to:

• resolve #
• not resolve anything else (with node-resolve)