Bug 439684

Everybody knows that you can "hide" a file by naming it with leading dot. But this is often inappropriate and you want a deeper control of managing what is hidden and what is not.

There is a mechanism for hiding files/folders that are not starting with dot. You create a file named ".hidden" in the directory of interest, write there file names line by line. And effectively hide unwanted files.

But currently, there is no mechanism to do the opposite thing. You may want to force keep some dot files to be visible even after you disable viewing of hidden files with ctrl + h.

I suggest adding that second half of the controlling mechanism.

STEPS TO REPRODUCE
I have a project folder (git repository). There is a subfolder "__pycache__" and I want to keep it always hidden. And there is ".SRCINFO" file and I want it to be always visible (because I want to comfortably see when it changes, the git plugin in dolphin marks changed and unchanged files).

OBSERVED RESULT
I am unable to do so. I either see the unwanted "__pycache__" (while checking if .SRCINFO changed) or I do not see ".SRCINFO" (while hiding unwanted __pycache__).


EXPECTED RESULT
Like in .gitignore, I think it is good to support "!" at the beginning of the file name to mark opposite meaning. So adding the file ".hidden" to the folder of interest with the following content should solve the task:

```
__pycache__
!.SRCINFO
```

SOFTWARE/OS VERSIONS
Operating System: Arch Linux
KDE Plasma Version: 5.22.3
KDE Frameworks Version: 5.83.0
Qt Version: 5.15.2