Generate plugin assets for json files

One more topic on missing plugin assets:

Are only assets of a certain filetype moved (or aliased) to the media/ folder ? Or all (as I previously expected)? When I try to access various assets I need for my Plugin, I found out, that at least in my case, only some assets are moved to the media folder:

$path = 'media/plugins/my-name/plugin-name';

// correctly moved to the media folder
echo url( $path . "/test.png" );
echo css( $path . "/test.css" );
echo js(  $path . "/test.js" );

// correct url is printed, but file not moved to media folder, 404
echo url( $path . "/test.css" );
echo url( $path . "/test.js" );
echo url( $path . "/test.json" );
echo url( $path . "/test.txt" );
echo url( $path . "/test.unityweb" );

So in case of the css file: It is moved when using the css() function, but not with url(). While url() does work for the image file.

However, I just need the correct URL, nothing else. And therefore, the file has correctly be aliased/copied to the media folder.

Do I have to do it manually for those file types such as json, … or should that happen automatically? Do I have to register those filetypes somewhere?Am I missing something? Or is there another recommended way to access “special” plugin assets?

Thank you very much for your ideas!