feat: Make the "Folders" tree view searchable with a text pattern

[soenkehahn]

Is your feature request related to a problem? Please describe.

I'm using the "Folders" view (specifically "Server Folders"), since I do have my music fairly nicely organized in the file system. I know what folder I want to navigate to, but then I have to manually scroll around in the (alphabetically sorted) tree view to find the one I want.

Sometimes I just know part of the folder name, but I might misremember the full folder name. Then the alphabetical sorting isn't even that helpful. (For example I was looking for a folder called 'Beethoven', but couldn't find it. I realized the folder is called 'Ludwig van Beethoven'.)

Describe the solution you'd like

I would love to have a text search field that I could use to filter the first level of the tree view. So if I typed a search pattern into the search text field, it would filter out all toplevel folders (and their children) that don't contain the given text. The search should be case-insensitive.

I often listen to entire albums of some artist and my folder structure is ./$artist/$album. This would make it very convenient to search for an artist, list all their albums and then drag one into the playlist.

Describe alternatives you've considered
I've tried using the "Search" view. Unfortunately that makes adding full albums fairly cumbersome: If I search for an artist name, it shows me all tracks of that artist in a flat list. I then have to manually select all the tracks of an album to add it to the playlist. This gets more cumbersome when my search term also matches unrelated song or album titles.

I've also considered using the "Library" view. The problem with that is, that I have a bunch of songs in my music collection that are the only (or a few songs) of that artist that I have. I've curated the collection on the file system, so that all these artists don't show up at the top-level, but all these single songs are stowed away in some directory. But in cantata's library all artists of all songs in my library show up at the top-level.

Additional Context
I have my music files structured in the way I like them to be structured on the file system. So I would like my music player ui to just give me a nice way to browse the file system. cantata's "Folders" view is already really nice for that, but this feature would make it even better.