[1.4.0] Add a search filter for scroll velocity changes

[faluhub]

This pr adds a search filter for the amount of slider velocity changes in a map. Its short name is svc. Must refresh beatmaps before results show up :)

[AiAe]

I think this needs to be improved to ignore scroll velocities at 1.00x, because they are marked falsely as scroll velocity.
For example this map will show when searching for svc>0 https://quavergame.com/mapset/map/16

[Emik03]

Wouldn't this also include osu! normalization SVs, so you can't just say "ignore 1x", it must be "ignore perceived 1x-ish". (rounded due to floating points)

[Illuminati-CRAZ]

Clearly we should implement an SV difficulty calculator for this

[Illuminati-CRAZ]

On a serious note, I personally don't think we should add scroll velocity count as a thing to filter by. A bunch of "normal" maps will be would be filtered out by "svc = 0" because they use SVs for BPM normalization, and at higher sv counts it stops being a good metric for distinguishing between SV maps.

[AiAe]

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