Add api mapping dump feature to AIDL files

The aidl compiler can process files and dump mappings between JNI
signatures of generated methods and their corresponding position in
.aidl source files.

Test: make aidl-mappings
Change-Id: I256cfc50967a1781f6a26064263d5f623612d40e
diff --git a/Android.bp b/Android.bp
index 8cb298d..0deee8d 100644
--- a/Android.bp
+++ b/Android.bp
@@ -57,6 +57,7 @@
         "generate_ndk.cpp",
         "generate_java.cpp",
         "generate_java_binder.cpp",
+        "generate_aidl_mappings.cpp",
         "import_resolver.cpp",
         "line_reader.cpp",
         "io_delegate.cpp",