console: manually map numeric keypad (KP*) bindings

While mpv normally uses the text a key produces (as opposed to physical
key mappings), this is different with the keypad. This is for the sake
of making it possible to distinguish between these keys and the normal
number keys on the left side of a full size keyboard.

There were complaints that the keypad doesn't interact with console.lua,
so manually map them. This ignores numlock (behaves as if it's always
on), and maps KP_DEC to "." (even though it's mapped to "," on some
keyboards). The /*-+ keys produce ASCII on mpv (at least with X11) as an
inexplicable inconsistency, so there are no mappings for these.

Fixes: #7431