type definitions for lib mode

[FDiskas]

I know there were a lot of discussions, but the problem still exists.
We all would like to have one tool to do everything. A similar example would be "parcel", "microbundle" bundlers.

So the problem is that currently, you need a separate process/script/config to build a type for your awesome library.

The Idea 💡 would be for vitejs - if this is library mode take a look at package.json and see if there is a "types" key in json - that would mean to enable type generation after build to the specified file path.

Take a look at tsup builder - it uses rollup plugin for generating type definitions
https://github.com/egoist/tsup/blob/6de0e4a14a5781eea8e59cf333bca7098e247d52/src/rollup.ts#L16

It could be solved in a similar way - right?