[Workspace] Make revision optional in edit method
[Workspace] Make revision optional in edit method

Otherwise we need to check if dependency in already in edit mode at the
call sites which is waste because this method already does that.

JGiola/swift-package-manager,sschiau/swift-package-manager,abertelrud/swift-package-manager,apple/swift-package-manager,sschiau/swift-package-manager,sschiau/swift-package-manager,vmanot/swift-package-manager,JGiola/swift-package-manager,abertelrud/swift-package-manager,abertelrud/swift-package-manager,JGiola/swift-package-manager,vmanot/swift-package-manager,abertelrud/swift-package-manager,sschiau/swift-package-manager,apple/swift-package-manager,apple/swift-package-manager,apple/swift-package-manager,JGiola/swift-package-manager,vmanot/swift-package-manager,apple/swift-package-manager,sschiau/swift-package-manager,abertelrud/swift-package-manager,vmanot/swift-package-manager,JGiola/swift-package-manager,vmanot/swift-package-manager