Replace default export with named exports (#1998)

## Launch Checklist

See title,
Also removed some "_" from some file names.
This is a pure refactoring, no logic changes.


 - [x] Briefly describe the changes in this PR.

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

src/components/Doc.tsx

@@ -23,7 +23,7 @@ type DocProps = {
   }
 };
 
-export default class Doc extends React.Component<DocProps> {
+export class Doc extends React.Component<DocProps> {
   render () {
     const {fieldSpec} = this.props;