Add saved beatmap filter functionality with popover UI

[Sayrix]

Add the ability to save and re-apply beatmap selection filters in Song Select (SelectV2). It introduces a small popover UI accessible from the search box area, allowing users to:

• View saved filters (per ruleset)
• Apply a saved filter to the current controls
• Save the current filter state under a custom name
• Delete saved filters

Related discussions: #30403, #13010

video2.mp4

This is my first contribution to this repository and also my first experience with C#. Thanks in advance for your time and feedback!

[pigeonskew]

This is amazing and will definitely be used by a lot of players IF it's obvious enough.
Currently, that search button isn't that noticeable due to how it kind of "blends" in the overall design, that I'm certain players won't even try to hover their cursor on that icon (also since players just need to type right away to search).

I suggest to change that search icon's design/color a bit so that it can stick out a bit more on the naked eye and have more players be aware of this feature.

[peppy]

Why does clicking a filter keep the menu open while deleting closes it?

A starting point would be to use existing design cues rather than make something completely new feeling. Maybe the collections dropdown is a good place to start? It matches design language and also features a custom button.

[Sayrix]

I tried adding a new drop-down menu next to collections, but it took up too much horizontal space and made the header too cluttered, so I placed the control in the search button instead. In addition, the collections drop-down menu uses a slanted layout and darker colours, so rather than using this visual in the search area, I made a variation that I think fits better with the search visual.

[peppy]

As long as it's in the filter control, I believe you need to match the skew. It doesn't have to be an actual dropdown, but should be styled to fit.

[Sayrix]

Deleting a saved filter now keeps the menu open, and the menu is slanted to better match the current style.

video2.mp4

[Joehuu]

This doesn't follow other popover button state behavior (i.e. pressing down the button should close the popover and pressing up should open it again). Should be consistent even if I find the behavior weird as many others in the below discussion have.

Ref: #33387

[Sayrix]

The behavior when pressing the button is now the same as other popovers

video3.mp4