Migrate from FlatSpec to AnyFlatSpec

Proprietary

Renames FlatSpec to AnyFlatSpec in extends clauses and updates the import from org.scalatest.FlatSpec to org.scalatest.flatspec.AnyFlatSpec (ScalaTest 3.x).

org.openrewrite.scala.testing.MigrateToAnyFlatSpec
mod run . --recipe=org.openrewrite.scala.testing.MigrateToAnyFlatSpec

Install it once from Recipe actions, then run it on every repository under the current directory. New to the Moderne CLI? Set it up.