Add .jar tag to java modules

Allow java modules to be referenced as ":module{.jar}" to get
the classes .jar.

Bug: 122333007
Test: m checkbuild
Change-Id: I2d07f774ae8ed5a39206059c4102727c6802d26e

java/java.go

@@ -355,6 +355,8 @@ func (j *Module) OutputFiles(tag string) (android.Paths, error) {
 	switch tag {
 	case "":
 		return append(android.Paths{j.outputFile}, j.extraOutputFiles...), nil
+	case ".jar":
+		return android.Paths{j.implementationAndResourcesJar}, nil
 	default:
 		return nil, fmt.Errorf("unsupported module reference tag %q", tag)
 	}