Revert "Remove unused container type"

This reverts commit 8aa68c0.

module.go

@@ -28,6 +28,16 @@ import (
 	"go.uber.org/fx/internal/fxreflect"
 )
 
+// A container represents a set of constructors to provide
+// dependencies, and a set of functions to invoke once all the
+// dependencies have been initialized.
+//
+// This definition corresponds to the dig.Container and dig.Scope.
+type container interface {
+	Invoke(interface{}, ...dig.InvokeOption) error
+	Provide(interface{}, ...dig.ProvideOption) error
+}
+
 // Module is a named group of zero or more fx.Options.
 func Module(name string, opts ...Option) Option {
 	mo := moduleOption{