Typescript types

[jankapunkt]

Summary

Adds TS types, attempt to replace #192 as it's CI is failing

Linked issue(s)

191

Involved parts of the project

build

[jankapunkt]

@pierophp please review this shortly.

I changed some things here, which seemed to be missing:

• the are now not linked via exports but via types in package.json, according to the TS documentation
• the rollup copy only needs a folder as destination, not the filename, otherwise it would create another nested folder with the filename as foldername and place the file in there

[pierophp]

@jankapunkt It looks good! Thank you!