Add the file type (language id) to the status line

[usagi-flow]

This is a tiny little change that adds the currently detected file type (i.e. the document's language id), and falls back to "text" if none is detected (e.g. when a scratch buffer is opened).

I didn't notice any localization around so I just hardcoded the text "text".

PS: I'm also playing with the idea of using an icon for each detected file type (à la devicons), let me know if that'd be a welcome change.

[the-mikedavis]

There's a similar PR in the queue: #2211

The devicon stuff may be good for a plugin but since they tend to require patched powerline fonts, it's not a good fit for core.

IMO just showing the language ID or scope plus maybe the LSP name is a good fit for core 👍

[archseer]

For me this falls under #708, it's something that should be configurable and I don't want to always see it by default. It just clutters the status line because most of the time you already know the file type, and if you don't, it's one command away.

[the-mikedavis]

Should we close this in favor of #2434?

[usagi-flow]

Should we close this in favor of #2434?

I think that would make more sense. I implemented #2434 as a result of this PR, and I already included the support for the file-type status line element, so I guess that's where the show goes on.

I'll close this PR, thank you for your feedback!