fix(babel-plugin-export-metadata): add case for export default memo()

[yoo2001818]

Description

babel-plugin-export-metadata currently doesn't handle using call expression inside export default, such as:

export default React.memo(Component)

This means it won't include __filemeta in the default export, so <Props> won't work correctly because it can't resolve the file path.

It resolves such case by separating expression and export default, to allow injecting __filemeta correctly.

const __DOCZ_DUMMY_EXPORT_DEFAULT = React.memo(Component)
export default __DOCZ_DUMMY_EXPORT_DEFAULT

[yoo2001818]

I wasn't able to reproduce this problem in development build, probably because hot loader already rewrites code like this. However, production build doesn't include __filemeta.

Before 9d5b129#diff-5cc2196461930cb24939fb44764d656b, lack of __filemeta simply ended up not showing Props (Because componentName was null). However, after that commit, it broke production build - it threw an error.

The reason was somewhat weird - pascal-case package throws an error when null is passed. At first, I tried to resolve the problem by adding simple null check like pascalCase(componentName || ''), but I thought it was better to fix the fundamental problem.

[rakannimer]

Thanks @yoo2001818 for the PR !