GraphicsChoice is used by the panes in the Graphics config window to
create combo boxes that change their associated config setting, and
update their own state when something else changes the config setting.
Despite its current name nothing about this class is particular to the
Graphics window, so renaming it to ConfigChoice better reflects its
purpose. This should also make it less confusing when ConfigChoices are
eventually added to the other config windows.
Before, Free Look would accept background input by default, which means it was easy to accidentally move the camera while typing in another window. (This is because HotkeyScheduler::Run sets the input gate to `true` after it's copied the hotkey state, supposedly for other threads (though `SetInputGate` uses a `thread_local` variable so I'm not 100% sure that's correct) and for the GBA windows (which always accept unfocused input, presumably because they won't be focused normally).
SPDX standardizes how source code conveys its copyright and licensing
information. See https://spdx.github.io/spdx-spec/1-rationale/ . SPDX
tags are adopted in many large projects, including things like the Linux
kernel.
