City Ballet is delving into its spring season with a celebration of new growth in ballet. The first few nights feature three different but equally enticing programs of 21st-century choreographers, including Justin Peck, Alexei Ratmansky, Benjamin Millepied, William Forsythe and Christopher Wheeldon. JR, the French artist who brought us the expansive photo installation on the floor of the David H. Koch Theater promenade, makes his first foray into choreography with "Les Bosquets," appearing on all three programs. Created with the help of the company's artistic director, Peter Martins, the work features the Memphis jookin' virtuoso Charles Riley (better known as Lil Buck) in his Lincoln Center debut, an original score by Woodkid and 40 company dancers.