PathColumn : Allow sorting of FileIconPathColumn

[murraystevenson]

This makes the FileIconPathColumn sortable via the CellData::sortValue property. This sorts by file extension, which is an approximation of sorting by file type, but is likely enough for our purposes.

@ericmehl In light of #6006, do you think we will need similar special handling here for non-english characters on Windows?

[johnhaddon]

I think this is fine (pending Eric's input on the Windows side), but I wanted to mention one thing in case it appeals at all : you could use the Qt API internally here if it's easier or better. The reason we couldn't do that for FileIconColumn is that it would have meant passing Qt types through the CellData API, but that's not necessarily a problem here if we can distill an int or string from the Qt query.

[murraystevenson]

I wanted to mention one thing in case it appeals at all : you could use the Qt API internally here if it's easier or better...

Thanks, definitely worth considering. We could potentially use QMimeDatabase for this, though sorting by MIME type may be less useful than sorting by extension: .gfr, .txt, and .usda files would all sort together as they'd all likely identify as "text/plain". The most robust might be some combined sort value like extension:mimetype:stem, but the current extension:stem is likely useful enough...

@ericmehl any Windows concerns that we should address before merging? The latest push is just a rebase to resolve the Changes.md conflict.

[ericmehl]

@ericmehl In light of #6006, do you think we will need similar special handling here for non-english characters on Windows?

I think we should be fine on this PR. Sorting non-English characters on Windows will work out the same as on Linux (once #6006 is solved and merged) since we'll be converting to UTF-8 (same as Linux uses throughout) in FileSystemPath itself, before the PathColumn sees the value.

So LGTM from that perspective.