[problems] Implemented clear-all in problems view.

[Anasshahidd21]

What it does

Fixes: #7979

Added a Clear-All toolbar item, which clears all the existing problem
markers

Tested the icon doesn't leak to other views such as:

1. Terminal
2. Output Channel
3. Search in Workspace
4. Extensions.

Signed-off-by: Anas Shahid muhammad.shahid@ericsson.com

How to test

1. create multiple json files, with lorem ispum, it will generate problem markers
2. Click on the icon on the toolbar to clear all the markers.
3. Close the file and re-open it to see if the markers are present.
4. Test to see if the icon is leaking to any other view.(like siw)

Review checklist

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

Reminder for reviewers

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

[akosyakov]

Please make sure that toolbar item does not leak to other views, i.e. isEnabled and isVisible are respecting the current widget. (if it is not the case yet)

[kittaakos]

I have verified it in Gitpod; it worked as expected. Thank you, @Anasshahidd21 👍

Note: When I execute the Reset Workbench Layout command, the Problems view is opened, hence the command is enabled, but the bottom panel is toggled, so one cannot eventually see the Problems view. Strange UX; this has to be addressed in a separate issue if we want to change it.