Fix duplicate files and other recent regressions

[jeremypw]

Fixes #2190
Fixes #2189
Fixes #2188

This PR "completes" the faulty commit responsible. The file-rowreference map was not being updated in all relevant places .

The map must be updated whenever a file is added or removed from the model, not just on loading.

NOTE: This PR and the previous one only speed up construction/destruction of the model. The most dramatic speed increase is seen when the Directory is cached and does not have to be reloaded from disk. Loading/sorting a large directory for the first time can still take several seconds (exponent >1 and <2) and there is a noticeable lag when navigating away.

On a modestly powered machine folders containing several thousand item are acceptably responsive, but tens of thousand items still result in significant delays (with no user feedback).

The GTK4 port is already much faster so probably not worth spending too much time improving the Gtk3 version?

[peteruithoven]

Great! This seems to at least fix:

• Can't rename single file #2189
• Segmentation fault when trying to create/delete file(s)/folder(s) #2188

Not sure about #2190. I noticed that with the master branch it duplicated files created outside of Files. With this PR that no longer happens.

[ryonakano]

I can't confirm #2190 at all although I browsed a folder with 100 files (which I created by for i in {1..100}; do touch test$i; done;) so not sure if this branch fixes it, but can confirmed this branch fixes the others.

[jeremypw]

I can't confirm #2190 at all although I browsed a folder with 100 files (which I created by for i in {1..100}; do touch test$i; done;) so not sure if this branch fixes it, but can confirmed this branch fixes the others.

I observed this issue on a slow computer - I have now tried to reproduce on a more modern faster computer without success so must be a race of some kind.

[jeremypw]

@ryonakano Thanks for the review and suggestions, which I have now addressed.

[ryonakano]

Looks good to me and works confirmed, thank you for your fix!