When a new file is opened the CodeChecker analysis should be started in the background

[dkrupp]

When a new source file is opened, the analysis (if not up-to-date) should be automatically executed in the background and the results shouldbe shown in the "reports in current file" tree.

Today, the analysis is not started, only after the "Re-analyze current file" button is pressed.

[dkrupp]

We concluded that if we reanalyzed the files always upon file opening that would to too resource consuming. So instead the vscode plugin should show in the codechecker window that the files "has never been analyzed" or the "analysis is out of date". This needs improvements in CodeChecker see https://github.com/Ericsson/codechecker/issues/4100