Show proper default key name in reset tooltip on keybindings menu

[CrazyladMT]

Fixes #16515

This PR fixes an issue in the keybindings menu where the reset button shows a cryptic tooltip such as "Reset setting to default (SYSTEM_SCANCODE_##)".

This also adds a new core function for the main menu core.get_key_description() to take a scancode and convert it to the human-readable name that is already available in KeyPress.

To do

This PR is Ready for Review.

How to test

1. navigate to the keybindings menu inside settings
2. set a keybinding
3. hover over the reset button and observe that it shows a human-readable key name

[SmallJoker]

Does work. At least as long as the key exists.

According to https://wiki.libsdl.org/SDL3/SDL_Scancode , respectively the USB standard https://gist.github.com/mildsunrise/4e231346e2078f440969cdefb6d4caa3 this should refer to the + key, which does not exist on my keyboard.
Fair enough. Works.

[y5nw]

LGTM

[y5nw]

Does work. At least as long as the key exists.

According to https://wiki.libsdl.org/SDL3/SDL_Scancode , respectively the USB standard https://gist.github.com/mildsunrise/4e231346e2078f440969cdefb6d4caa3 this should refer to the + key, which does not exist on my keyboard. Fair enough. Works.

This is the key to the left of the backspace key, which is a dead key on some layouts (dead acute on the German layout, dead circumflex on a Swiss one). SDL does not report a keycode for this, so the scancode is displayed.

[y5nw]

Tested and works