Madison Square Garden, New YorkThe millennial-beloved pop star brings the house down in an emotional and energetic chance to show off her new, return-to-form album“What does freedom feel like?” the singer Kesha asks in voiceover early in her sold-out show at Madison Square Garden on Wednesday night. The 38-year-old pop star has just opened her “Tits Out” show with TiK ToK, the sleazy, insouciant, inescapable party anthem that rocketed her to fame in 2009, cradling a model of her own head from that time – blond, dead-eyed, distinguishable as the artist formerly known as Ke$ha by one single glitter tear. She paraded the head while gamely barreling through that first indelible, now altered, lyric – “wake up in the morning like FUCK P Diddy” – and the IDGAF brag of brushing her teeth with a bottle of Jack (Daniels). Then she places it on an altar of empty glasses and candles and bows to a prayer of “freedom from my past”, how the “truth will set you free”.If this all seems like a lot, somehow both cartoonishly blunt and muddled, hedonism strangely crossed with sanctity – well, that’s Kesha, a millennial-beloved artist always on the messy bleeding edge of culture, for better and for worse. Once the 22-year-old from Nashville who rolled in on her gold Trans-Am and glittered-bombed the early 2010s with a ridiculous string of feral, slangy hits, then a cautionary tale stalled by a nearly decade-long