Avoid shipping src

[ArnaudBarre]

Good call on moving typing of plugins in a separate @types alias + support from plugin themself via module declaration, install size was one of the main reason I didn't add the lib to the React templates. I've looked at the v2 output and I see that src is shipped and doesn't bing more than dist it seems. Also not sure about the tsconfig there, it sometimes make tsc behaves strangely.