This allows the new parser package to be used in TypeScript projects, with static type checking and auto-completions. IDEs like VSCode will use this to show auto completions even in JavaScript projects, which is a huge benefit to users wanting to use the parser directly.
This PR follows the auto-generated .d.ts that was added to @babel/types in #7101
- took outdated DefinitelyTyped babylon .d.ts and updated it using new site's documentation.
- added "typings" folder to package, with the new .d.ts
- connected new .d.ts via package.json's "types" field. also adjusted "files" so folder will be published.
- definition file uses TypeScript 2.9's new `import('package').Type` syntax.
