DO NOT MERGE Add --srcjar option to  mojom_source_generator.sh

This is essentially a cherry-pick of
https://android-review.googlesource.com/c/699550.

Bug: 110444246
Test: build
Change-Id: I7579f91c760a6b4380861390109a12298da2703d
diff --git a/soong/mojom_source_generator.sh b/soong/mojom_source_generator.sh
index f1fac9e..a63b8a0 100755
--- a/soong/mojom_source_generator.sh
+++ b/soong/mojom_source_generator.sh
@@ -71,6 +71,10 @@
     --generators=*)
       generators="${arg#'--generators='}"
       ;;
+    --srcjar=*)
+      srcjar="${arg#'--srcjar='}"
+      srcjar="$(get_abs_path ${srcjar})"
+      ;;
     --*)
       args=("${args[@]}" "${arg}")
       ;;
@@ -110,3 +114,7 @@
     unzip -qo -d "${output_dir}"/src "${output_dir}/${rel_path}".srcjar
   fi
 done
+
+if [[ -n "${srcjar}" ]] ; then
+  (cd "${output_dir}/src" && find . -name '*.java' -print | zip "${srcjar}" -@)
+fi