BOSTON — Maine could be the next New England state to embrace same-sex marriage after the State Senate voted Thursday to legalize the practice. The Democratic-controlled Senate voted 21 to 14 for a bill that would allow gay couples to marry starting later this year. The measure appears to have even broader support in the House of Representatives, which will take it up on Tuesday. Gov. John Baldacci, a Democrat, used to oppose same-sex marriage. But since the bill was introduced in January, he has said he is keeping an open mind.