osk: Move return key in five-row layouts from the second to the third row
This is a follow up from my proposed commit here !1427 (96e27f9a) to move 'ฃ/ฅ' key in Thai layout from the third to the second row, which was not merged because this change would also require the return key to move from the second row to the third row. (As in this image, and also see the reference spec TIS-820)
Since, according to !1427 (comment 1035458), moving the row of return key would benefit other five-row layouts as well, GNOME on screen keyboard should support this.