Culture was not taken into account when parsing filters, which meant
that in cultures that use the comma (,) as a decimal delimiter, it would
conflict with the comma used to delimit search criteria. To remove
any ambiguity, introduce local helper functions that allow the decimal
point to be utilised, using the invariant culture. This also matches
stable behaviour.
The decision to not reuse osu.Game.Beatmaps.Formats.Parsing was
deliberate due to differing semantics (it's not really sane to throw
exceptions on receiving user-facing input).