Create a method for getting the MIME type for a file extension from a map

As is, this MR would break BC if something is overriding the file.mime_type.guesser.extension service class. (The Sophron guesser module does that, https://git.drupalcode.org/project/sophron/-/blob/2.1.x/sophron_guesser/...)

I think we should use a deprecation helper to introduce usage of the new method ::getMimeType() based on its existence in the implementation class.

Hmm. I didn't realise how this was being used.

I think we should use a deprecation helper to introduce usage of the new method ::getMimeType() based on its existence in the implementation class.

I'm not sure about that approach.

It might be better to add a new interface and service and switch that out with a BC layer.

Blast from the past, 🐛 Separate MIME type mapping from ExtensionMimeTypeGuesser Needs work .

That one getting stuck led me develop the Sophron module.