Add aidl file support to java builds

Add support for aidl files listed in srcs for java builds, and
an aidl_preprocess module type for framework and sdk aidls.

Change-Id: I3aa537f4483822e5b534c74d0b35f13a938f8947

java/builder.go

@@ -97,6 +97,7 @@ type javaBuilderFlags struct {
 	dxFlags       string
 	bootClasspath string
 	classpath     string
+	aidlFlags     string
 }
 
 type jarSpec struct {