Enable setting and updating diagnostics on a single quickfix list(diagnostics)

[ajayvigneshk]

The code appears working. But I see the orginal code (left untouched) is also referenced by other parts. Need to know if those also need to be updated. Fixes this: #951

[martskins]

@ajayvigneshk sorry that it took this long to get an answer for you but if you are still interested in getting this merged and are willing to rebase this to dev branch I can give it a try and get it merged. It definitely sounds sensible.

[ajayvigneshk]

@martskins This PR is raised against next branch. Should I raise a new PR if I rebase my changes onto dev?

[martskins]

@ajayvigneshk You can just change the target branch of this PR if you click on the edit button next to the title. That, plus rebasing your branch to dev should do it.

[ajayvigneshk]

@martskins Done. Thanks for the tip.