Show previous/next diagnostic with phantom

[tomv564]

Press F8 to open/next, shift+F8 for previous, esc to close. (see suggested keybindings)

Essentially like VS Code's "Next Problem" feature.

Suggested keybindings

{ "keys": ["f8"], "command": "lsp_next_diagnostic"},
{ "keys": ["shift+f8"], "command": "lsp_previous_diagnostic"},
{ "keys": ["escape"], "command": "lsp_hide_diagnostic", "context":
	[
		{ "key": "setting.lsp_diagnostic_phantom"}
	]
}

Closes #746:

• Allows navigation for those who don't like to use the panel for it (SublimeLinter style)
• Allows a faster and more readable way to see a diagnostic + related info than hovering.

Implementation details:

• The DiagnosticsPresenter passes user actions (forward/back) and server diagnostic updates into the DiagnosticsCursor
• The cursor selects a different walking logic based on an already-selected diagnostic or a cursor position in a file.
• The Escape key is "stolen" if the view has a lsp_diagnostic_phantom setting applied. There is some risk with stealing a so often-used key.
• Phantoms are not hidden if a diagnostic disappears.

To do:

• Implement UI + wire up Esc for dismissing phantoms
• Implement UI for related info
• Update UI for code actions (if keeping at all)
• Review behaviour when diagnostics removed/moved/added.
• Only include warnings and errors (See Don't show hint diagnostics in problems view? microsoft/vscode#45436)
• UI polish (add prev/next, related info spacing and color, top arrow, rounded corners?)
• Organize diagnostics code and add unit tests

[coveralls]

Coverage increased (+1.9%) to 37.886% when pulling 6a8757c on select-and-phantom-diagnostic into 75fe01c on master.

[rwols]

I haven't really looked at all the code yet, but I noticed these two things:

1. 
   The whiteish/bluish box around the related diags is not present. Is this intentional? It feels to me as if this part should share the same css code as the hover popup.

2. The command lsp_next_diagnostic does not cycle back to the beginning of the phantoms list, but lsp_previous_diagnostic does cycle forward to the end of the phantoms list if invoking it on the first diag. I think they should both have the cycle behavior.

[rwols]

see above comment

[tomv564]

Good catch, even had a TODO for testing the missed wrap-forward from diagnostic logic

The color was doable in this manner:

But I feel the extra markup/css is a bit unfortunate.
The amount of styling on hovers gets a little distracting, like this example:

For me the additional info is part of the error and could just be red.

[rwols]

For me the additional info is part of the error and could just be red.

I'm okay with having it red, but IMO there should be some sort of separation between the main diag and the related diags. Indentation for the related diags perhaps? Or a horizontal line? It's otherwise too vague (for me, probably also for other users) what the actual problem is, and what "additional info" is.

[tomv564]

I like your suggestion of the horizontal line a lot (I tried indent too but this is more space-efficient)

If you also think this looks good, then I will apply the same change to hovers

[rwols]

Looks good!

[tomv564]

I will merge this now and document it when we get to a release soon!