Branch :
`xkb_keymap_new_from_names`: Allow only one group per key in symbols sections. While the original issue was [fixed in `xkeyboard-config`](https://gitlab.freedesktop.org/xkeyboard-config/xkeyboard-config/-/merge_requests/253) project, the previous handling in `libxkbcommon` of extra key groups was deemed unintuitive. Note: rules resolution may still produce more groups than the input layouts. This is currently true for some [legacy rules in `xkeyboard-config`](https://gitlab.freedesktop.org/xkeyboard-config/xkeyboard-config/-/blob/6a2eb9e63bcb3c52584580570d31cd91110d1f2e/rules/0013-modellayout_symbols.part#L2).