Allow retrieval of WordPress media types and their extensions

[flixos90]

There have been a couple of occasions where I needed to access the list of media types and their file extensions that WordPress bundles. Unfortunately this list is only generated within the function wp_ext2type() and cannot be accessed from the outside.

A use-case is when I wanted to create a file upload field in a form builder plugin, I would like the admin to be able to select the required file type, and for that I would like to use the list from that function. Then I could check for the extensions / their MIME types whenever an upload through that field would happen.

I would propose to introduce a separate function that returns this list of media types and their file extensions. This function could then be called in wp_ext2type().

[flixos90]

Introduce wp_get_type_extensions() and a corresponding filter

[flixos90]

36294.diff​ introduces a new function wp_get_type_extensions() that returns the list and calls that function from wp_ext2type().

I also included a new filter to adjust this list. At first I wondered whether we should move the original filter ext2type into the new function, but I felt this would not be appropriate in terms of naming conventions. ext2type would now only adjust the types for the wp_ext2type() function while the filter wp_type_extensions would be applied globally.

[flixos90]

This can be closed as it's partly a duplicate of #35987 and was fixed in 37189.