Add current beatmap info to window title

[zihadmahiuddin]

I have tested it on Linux, both on Wayland and X11, using SDL2 and SDL3, and it's working fine for me.
It might need more changes as I'm still not super familiar with the codebase, but I thought I'd create a PR and continue here.

Closes #32188

[Susko3]

Test failures are relevant. Host.Window is null on headless tests.

[bdach]

Not sure about the following text being in the titlebar while the intro is playing out:

Feels kinda weird and is exposing our implementation details of "the intro music is a beatmap actually". Maybe this should be done in some other way to prevent this sort of stuff. Possibly hooked up to the UserActivity system that we use for online and presence and so on?

Need @peppy or @smoogipoo opinion on this.

[zihadmahiuddin]

I'm assuming all the "special" maps have their BeatmapSetInfo.Protected set to true, in that case maybe those can be ignored. It would be the easy fix but I don't know if it's the right one.
For now, I'm experimenting with UserActivity in another branch, would OsuGame still be the right place to track the current UserActivity?

[bdach]

I'm assuming all the "special" maps have their BeatmapSetInfo.Protected set to true

I forgot that this exists to be honest. We can use that too if it works, probably simpler that way.

[peppy]

Should only show during gameplay like stable.

[smoogipoo]

Lgtm