rules: add custom per-group mapping for level3(ralt_alt)

ralt_alt is a special mapping: "the right Alt key never chooses the third level." To achieve this, the key is defined for all four possible groups.

This causes an issue with the libxkbcommon parser which extends the keymap to be 4 groups wide thanks to this key, see https://github.com/xkbcommon/libxkbcommon/issues/262 That is arguably a bug in libxkbcommon whose behavior differs from xkbcomp - xkbcomp clamps to the number of layouts.

But defining the key this way is wrong, no other keys is defined for multiple groups on that purpose. The correct way to achieve this functionality is to define the symbols for group1 only and then adjust the rules so they automatically apply to all groups currently present.