Handle Wayland keyboard events and translate them to Windows events,
currently using a hardcoded US key mapping.

Fixes: bb6bcaf8

This partially reverts commit 0b7eed03.

glGetStringi() is not available before 3.0. We can't trust its
function pointer being NULL since the GL implementation is allowed to
return anything in this case (*cough* macOS's GL on Metal *cough*).

This probably regressed when fd92954d
removed the "if (!disabled[0]) return FALSE;" exit from
filter_extensions(), although that simply exposed an existing issue.

This partially reverts commit faae2162.