In what amounts to a kind of career-defining reunion, Jessica Chastain and Al Pacino will star alongside each other in “Lear, Rex,” a new big-screen Shakespeare adaptation of “King Lear” for filmmaker Bernard Rose (“Immortal Beloved”). Rose will write and direct, Pacino will star as the title character, and Chastain will star as Goneril, the eldest of King Lear’s three daughters.