“The Method: How the Twentieth Century Learned to Act” (out Feb. 1), theater historian Isaac Butler reveals how the Actors Studio, under the direction of the acclaimed late acting teacher Lee Strasberg, went on to shape the modern world’s most influential performers.Butler told The Post that despite what “method acting” has come to signify in pop culture — transforming yourself for a role, à la Daniel Day Lewis or Jared Leto, and living as that character for months or even years — it’s actually something entirely different.