Recover from solved errors in nested files without restarting develop

[karlhorky]

Summary

When errors occur within files within directories, the errors are reported on the command line and in the browser (this is good!). However, when the error has been resolved by removing the offending files, the errors do not go away.

Reproduction steps

1. Start a new site using gatsby new
2. Start the development server and navigate to a working page in the browser
3. Add a folder under pages with a JavaScript with an error in it (for instance, import blah from 'blah' - an import of a non-existent package)
4. The error appears in the browser and the command line
5. Remove the folder again
6. Refresh the page in the browser a bunch of times - the error appears intermittently until gatsby develop

Motivation

To prevent confusion about false negative error reporting.

Related

Maybe related to #14395

[karlhorky]

Maybe this is more of a bug than a feature request actually...

[karlhorky]

Seems really like a bug, resubmitted as such: #15722