scan all project for code warning, problems and errors.

### Description

I am not sure if this already implemented or not. But as I can see it is only show code warnings and code errors for the opened files only.
I hope there is a setting to scan all files once a project opened.

### Use case/motivation

_No response_

### Related issues

_No response_

### Are you willing to submit a pull request?

Yes

The issue names no files, tests, or entry points. Start by reproducing the current behavior with diagnostics in opened and unopened files, then trace how the project-open event and diagnostics are handled. Done means the intended setting or behavior is defined and diagnostics can be scanned across the project when it opens.

Written by the indexing model from the issue text.