Add "Clear missing files" option to recent ISO list

[italodirenzo93]

Description of Changes

Adds an option to the recent ISO list to remove all entries that can no longer be found in their original location.

Rationale behind Changes

Solution for #4963. I decided on using the term "prune" instead of "clean" because it sounds too similar to the existing "clear". Would welcome input on what the terminology for this function should be.

Suggested Testing Steps

1. Load an ISO file into PCSX2
2. In a separate file browser window, move that file to a different location on disk
3. Click the "Prune ISO list" option and the file will be removed from the list

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[lightningterror]

Maybe Clear invalid ISO list would make more sense.

[IlDucci]

Maybe Clear invalid ISO list would make more sense.

Or simply "Clear invalid ISO files". Maybe things could be made more obvious by referring to the entire ISO list (for the full removal, "Clean ISO list") and to the individual ISO files (for the pruning of only any missing ISO files, "Prune invalid ISO files").

[refractionpcsx2]

Or an even more user friendly way of writing it
Clear missing files

[nf6429]

Agree with the above. "Clear invalid ISO" to an end user could indicate something is wrong with your file itself, not that it's just been moved, whilst "clear missing files" directly states what the issue is.

[IlDucci]

Agree with the above. "Clear invalid ISO" to an end user could indicate something is wrong with your file itself, not that it's just been moved, whilst "clear missing files" directly states what the issue is.

Agreed as well.

[arcum42]

My main suggestion would be to show a list of what's going to be removed on the confirmation dialog box, before you actually remove it. Otherwise, I could see times where you could accidentally remove all or most of the entries because of something not being mounted at the moment...

[RedDevilus]

* Game1
* Game2
* Game3
These will be removed from the listing. Do you confirm?
OK              Cancel

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Should be feasible to do something like this.

[darkxex]

I find it very useful.

[italodirenzo93]

I agree. Will update the PR with a new commit soon.

Is it still recommended to use the wx* functions and types wherever possible instead of STL? (ex. wxFileExists vs std::filesystem::exists or wxString vs std::string).

I know the style guide says to prefer wx but I keep hearing that there's a QT rewrite planned and was wondering if that means there's less of a focus now on using the existing wx code?

[RedDevilus]

On your location you can't fully avoid WX but if you can, sure.

[lightningterror]

Commits should be squashed and properly named with prefixes.

[lightningterror]

Needs to be tested.

[arcum42]

Works properly, from what I can see.