Support wl_seat v7

wl_seat v7 only changes the following:

wl_keyboard::keymap

`From version 7 onwards, the fd must be mapped with MAP_PRIVATE by the recipient, as MAP_SHARED may fail.`

We have char *map_str = static_cast<char *>(mmap(nullptr, size, PROT_READ, MAP_SHARED, fd, 0));

Presumably because of that keymap CVE from a few years ago, I believe it should be safe to change even on old versions.