feat: Make the diagnostic picker display the resposible LSP

[RmStorm]

Solves #12474 and #11452

This should probably be configurable so my current approach is very naive. I just wanted to quickly whip something up for myself.

When programming in Python multiple/many LSP's is the norm and it can be hard to make sense of things. Hence this PR that displays the LSP responsible for a certain diagnostic in the picker.

[RmStorm]

This issue points out that diagnostics can be hard to read, particularly in the workspace diagnostics picker. I think my PR makes that worse..

Maybe I should check if there are multiple lsp's active? And then only display the source when that is the case?

[zetashift]

This issue points out that diagnostics can be hard to read, particularly in the workspace diagnostics picker. I think my PR makes that worse..

This is an issue I regularly deal with because I often have a sidepane open on a somewhat small screen. It kinda depends on what the maintainers say, but my 2c here is that:

• There is a PR that alleviates this concern by stacking the list and previewer: Stack picker and preview vertically if too narrow #13430 (I really hope this gets in somehow or some variant of this!!)

• One can press Ctrl+T to hide the preview and then the diagnostics become more useful in a smaller viewing area.

[the-mikedavis]

Yeah, this picker is quite crowded. Using C-t to hide the preview is the best way to see a bigger picture now. Maybe we can explore some ways to make C-t cycle through different 'views'/'modes' of the picker so that you only see the current column or something like that.

Hiding this column when there is only one language server active would make some sense at the moment but as we expand diagnostics to include things like spell checking we would need to remove that anyways.