Add java_genrules to use jars as inputs and outputs

Add a java_genrule that has the right multilib flags to be a
dependency of a java rule.  Make java libraries implement
SourceFileProducer so that their classes jar can be used as an
input to a java_genrule.  Allow libs and static_libs dependencies
to be a java_genrule.

Test: TestJarGenrules
Change-Id: Ib1b31ef9c0b7e72eeed2c9ecc4ce8a1088e0b1c9
diff --git a/Android.bp b/Android.bp
index 3e09add..643e8df 100644
--- a/Android.bp
+++ b/Android.bp
@@ -218,6 +218,7 @@
         "java/app.go",
         "java/builder.go",
         "java/gen.go",
+        "java/genrule.go",
         "java/jacoco.go",
         "java/java.go",
         "java/proto.go",