By Lucia Mutikani WASHINGTON, Dec 23 (Reuters) - The U.S. economy likely grew at a brisk clip in the third quarter, driven by solid consumer spending and business investment, but momentum appears to have since faded amid the rising cost of living and recent government shutdown. The Commerce Department's initial estimate of third-quarter gross domestic product on Tuesday is also expected to show the ​economy was supported by lower imports, which helped to curb the trade deficit. Much of the anticipated ac ...