Move typescript support out of individual packages

[ndelangen]

Who thinks it's a good idea to move typescript into separate packages / move to somewhere else?
I'm not typescript user myself, but want to continue support.

We should definitely do something right, because currently support is different over all packages.

[ndelangen]

Work on this is progressing well, It's on our roadmap/migration, I feel it's a bit redundent to keep an issue open for it.

It's a long process, and having an issue open that long isn't helpful.
https://github.com/storybooks/storybook/blob/b4d03d0d1c7f37616842e0ffe288815695ebcf5c/MIGRATION.md#moved-typescript-definitions