Add target for generating aidl mappings

Test: make aidl-mappings
Change-Id: If18cf25dbfb1b00d7bd39fd1e1032fd783fea792

Android.bp

@@ -1788,3 +1788,10 @@ filegroup {
     ],
 }
 
+// Creates an index of AIDL methods; used for adding UnsupportedAppUsage
+// annotations to private apis
+aidl_mapping {
+    name: "framework-aidl-mappings",
+    srcs: [":framework-defaults"],
+    output: "framework-aidl-mappings.txt"
+}