It was no longer possible to navigate listboxes (e.g. the server browser) by using keyboard hotkeys when no item is currently selected due to a regression from #6240.
Additionally, it was not possible even before #6240 to start navigating the server browser with the keyboard afer manually clearing the server address input, which is now possible as well.
Replace existing listbox implementations (`CMenus::UiDoListbox*` and `HandleListInputs` functions) with `CListBox` from upstream.
Reimplement additional feature that was already present in ddnet: page up/down, home and end key handling.
Affects the following lists:
- server browser
- server browser scoreboard
- server browser friends
- country / region selection popup (server browser filter)
- player skin list
- player country / region list
- theme list
- assets list
- graphics resolutions list
- dropdown menus (e.g. graphics fullscreen mode)
- ingame player list
- vote options list
- kick/specvote lists
- ghost list
- language list (in settings and in popup on first launch)
- demo browser
- editor file browser (saving, loading, adding images / sounds)
- The search / filename input is also improved so navigating a filtered list works correctly by porting the logic from upstream.
There are minor changes to the visual appearance of some lists, due to changed margins.
The vertical alignment of some list item texts is improved so the text is centered vertically.
