Improve parsing of artist/title from file names (+ tests)

[uklotzde]

The "smart" parsing of artist and title from file names should only be triggered for tracks without a title. Splitting into artist and title should only be applied if both artist and title are empty to avoid inconsistencies.

• Only parse track properties from file name if title is empty
• An empty artist should not trigger the file name parser because some tracks might not have an artist, e.g. sample sounds
• If the track already has an artist then the whole file name will be used as the title to avoid inconsistencies
• Move the parsing function into TrackInfo and add extensive tests that verify the intended behavior
• Preserve space characters in the file name and don't replace them by underscores in the resulting artist and title properties
• Only accept " - " or "_-_" as artist/title separators and not just a single '-' hyphen character
• Add an option (only in the code, no user setting) to prevent splitting into artist/title

Personally, I'm not a fan of this pseudo-smart parsing function and would simply copy the file name (without extension) into empty title fields, i.e. by setting splitArtistTitle = false independent of the artist field. But removing this function entirely might surprise some users, so let's keep and improve it slightly.

Some of the complaints (that this PR still won't fix as requested): https://www.mixxx.org/forums/viewtopic.php?f=3&t=12838

[daschuer]

Thank you for taking care. I have just a minor comment. The rest LGTM.

IMHO a better solution for the forum user would be to swap artist and title:

Stairway to Heaven 8'03 - Led Zeppelin (Led Zeppelin IV 1974 Atlantic)

but that is another story.

[daschuer]

Can we define " - " as well? This will avoid the assumption that only "_-_" is supported.

[uklotzde]

The discussion shows that this simplistic feature should have never been added. I had the pleasure to keep it alive during all the metadata rework and now once again. It solves a single, isolated use case and causes confusion for everybody else with a slightly different use case. I'm still convinced that simply using the file name (without the file extension that already becomes the file type) as the title would be the way to go, transparent and straight-forward.

[daschuer]

Thank you. LGTM.
I am quite happy that this feature exists though, because it helps me sometimes, especially since we write the metadata back.