Enable interprets with explicit `NoAction()`

[wismill]

Sometimes one may need to use explicit actions in the xkb_symbols section, but not for all levels. Levels without action must still be fill in with NoAction(). However, specifying any other action makes the whole group have explicit actions, resulting in interprets not triggering with levels with NoAction(), which is probably not intended.

Example:

xkb_keymap {
xkb_keycodes {
  <AD01> = 24;
  <LFSH> = 50;
  <RTSH> = 62;
};
xkb_types {
  type "TWO_LEVEL" {
    modifiers = Shift;
    map[Shift] = 2;
  };
};
xkb_compat {
  interpret Shift {
    action=SetMods(mods=Shift);
  };
};
xkb_symbols {
  key <LFSH> { [Shift_L] };
  key <RTSH> { [Shift_R, any], [NoAction(), LockGroup(group=2)] };
  key <AD01> { [q, Q], [a, A] };
};
};

<RTSH> will not activate the Shift modifier!

This is unfortunate, although it matches the xkbcomp behavior.

Since we now have VoidAction(), it would be better to trigger interprets iif there is no explicit action or on any explicit NoAction().

I think the impact would be minimal, but in doubt this can be limited to the keymap V2 format.