Add file extension-based plugin recommendation system

[mechatroner]

VSCode does this and I think this feature is convenient for users and helps to discover new plugins.
E.g. when someone edits .cpp file, Sublime Text can show a list of recommended C++ - related extensions.
When .py file is being edited - python related extensions are shown, etc.
Here is how VSCode suggestion box looks like:

Plugins in the list can be sorted according to the download count or some other criteria.

[FichteFoll]

FYI, there is currently no system in place for packages do denote their target programming language (or file extension) and it would be quite the effort to add this retrospectively for 3k packages. It could be automated for a couple of them (Syntax definition, programming language in package name), but that's about it.

Just to give you some perspective.

[mechatroner]

I can try to implement a script that would do automatic assignment when I have more time.
And to be clear, this system would never be "fair" because:

1. Some packages won't get any language assigned since they are language-agnostic e.g. "Sidebar Enhancements", theme packages, etc. So they would be never recommended (at least not with language-based recommendation system)
2. Some languages are more niche than others, e.g. Coconut-related packages would have much smaller chance to be recommended than C++ - related since *.coco files are just more rare.

Also thinking about this now, I am starting to understand that using just file extensions may not be good enough, since conflicts are possible e.g. *.pl can be used both for perl and prolog. So maybe a better option would be file extension + some file content-based model. I can think of "Bag of Words": https://en.wikipedia.org/wiki/Bag-of-words_model - It is very simple, easy to implement and reliable.