[plug-in][languages] Diagnostics are not represented in Problem view

[svor]

While using java VS Code extension I found that diagnostics are not represented in Problem view, so we can't see errors and warnings from the language server which was run by the plug-in.

[tsmaeder]

Can you see the diagnostic in the editor? How did you test this?

[svor]

In the editor I can see diagnostics with Error kind:

But no information in Problem view and no special decoration in Project tree

[akosyakov]

Editor, problems view and navigator use problem markers. If you convert plugin diagnostics to problem markers (not to Monaco diagnostics) they would appear everywhere.

[tsmaeder]

Correct, Diagnostics from the API do not go through the ProblemManager.

[akosyakov]

fixed by #4178