Change MIME type mapping for JavaScript to `text/javascript`

[mhankus]

Currently Spring maps js files to the application/javascript MIME type, as can be seen in mime.types.

According to https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics_of_HTTP/MIME_types#textjavascript

Per the IANA Media Types registry, RFC 9239, and the HTML specification, JavaScript content should always be served using the MIME type text/javascript. No other MIME types are considered valid for JavaScript, and using any MIME type other than text/javascript may result in scripts that do not load or run.

You may find some JavaScript content incorrectly served with a charset parameter as part of the MIME type — as an attempt to specify the character set for the script content. That charset parameter isn't valid for JavaScript content, and in most cases will result in a script failing to load.

Please update the mapping, so that JavaScript files are served in compliance with RFC 9239.