Enable unicode normalization on track data before matching
Normalizes the value of mainValue, artistValue and oneArtist with Qt provided normalization before it is compared to mFilterExpression's mFilterText and used for search. mFilterText is also normalized before it's being matched against.
With this fix the provided "Björk" file in the bug report is correctly found when searching "Björk" in the search bar.
I have read parts of the documentation of unicode normalization (https://www.unicode.org/reports/tr15/), but I'm not an expert
on the matter, so if someone knows that QString::NormalizationForm_C
would work better than the proposed QString::NormalizationForm_KC please let
me know.