Lady Gaga's been dodging Dr. Luke, refusing to be deposed in the Kesha case, but now he wants the judge to force her to do it ... TMZ has learned.   Dr. Luke filed docs demanding Gaga firm up a date when she will sit for the depo. In the docs, Luke says she tried to offer up a written statement instead ... but he says that's not good enough. He wants his lawyers to grill her face-to-face for no more than 3 hours. The hot topic Luke wants her to open about is a text message convo betwee