[markers] support 'information' diagnostic severity

[vince-fugnitto]

What it does

Fixes #5762: support information diagnostic severity (markers)

• add support for information diagnostic severity.
• populate the problems-view with info markers.
• add a statusbar icon for problems to reflect info markers if present

How to test

1. clone the repository (https://github.com/vince-fugnitto/vscode-extension-samples)
2. cd diagnostic-related-information-sample and perform npm i && npm run compile.
3. start Theia using diagnostic-related-information-sample as a workspace
4. perform F1 and Hosted Plugin: Start Instance and select diagnostic-related-information-sample
5. in the new hosted instance, open the file sample-demo.rs
6. there should be new info markers present from the file

In general, the guidelines from the following wiki was used.

Review checklist

• as an author, I have thoroughly tested my changes and carefully reviewed following the review guidelines

Reminder for reviewers

• as a reviewer, I agree to behave in accordance with the review guidelines

Signed-off-by: Vincent Fugnitto vincent.fugnitto@ericsson.com

[vince-fugnitto]

The PR is marked as a draft until I can successfully find an easy way for reviewers
to be able to test the new functionality and generate information markers.

[lmcbout]

@vince-fugnitto looks good
Question: Why not completing the Diagnostics list with the "Hint", they could be handle the same way as the information on the status bar. So if there is some "Hint" value, we add it to the status bar as well?
The "Hint are already added to list of markers in the problems view.

[vince-fugnitto]

Question: Why not completing the Diagnostics list with the "Hint", they could be handle the same way as the information on the status bar. So if there is some "Hint" value, we add it to the status bar as well?

The "Hint are already added to list of markers in the problems view.

I was thinking that adding hints would be too noisy too display on the statusbar.
(vscode doesn't display hints as well afaik, it looks like they are for editor purposes only)