Previously m_keysym was only updated on key press. This caused issues
when multiple keys are pressed at the same time. E.g., if the user
presses A, presses B, releases A, releases B, the actual events sent by
kwin was A pressed;  B pressed; B released; B released.

Also call xkb_state_update_key after xkb_state_key_get_one_sym, as
recommended by the libxkbcommon documentation