GH-2538: Fix for diagnostic/linting concurrency.

[dantleech]

Hopefully fixes #2538

This PR will:

• Fix a wrong assumption that the text document version should b e provided on save by the client. We now get the last known version from the Workspace.
• Do not run the linters if the text document (which may have been queued) is older than the last linted version of that document.

[artfulrobot]

Tried this. With mason in neovim, I still get several processes: one for each file I have open in nvim and another one.

[dantleech]

I still get several processes: one for each file I have open in nvim and another one.

it's still expected to get one per file - has this PR improved it at all? I guess even if we throttled it to one file you'd still be waiting for it to analyze the open files.

this PR should prevent having > 1 process running per-file unnecessarily.

i'm going to check the example given in the original issue and see if I can see what could make the diagnostics so slow.

[dantleech]

this has made it into master now anyway, so closing.