Add mechanism for adding new files to ojluni/annotations.

This change adds two new make targets which create empty stub files suitable
for copying into ojluni/annotations, which the developer can then annotate.

The instructions (and a description of the previously undocumented
mmodule subdirectory) are included in the README.

Bug: 64930165
Bug: 115746226
Test: Followed the steps added to the README
Change-Id: Iea070ffb97cd93731f24ba379fd3a38d0b70b9c6
diff --git a/openjdk_java_files.bp b/openjdk_java_files.bp
index 631348e..fe7b305 100644
--- a/openjdk_java_files.bp
+++ b/openjdk_java_files.bp
@@ -1805,3 +1805,31 @@
         ":openjdk_lambda_stub_files",
     ],
 }
+
+// Generates stub files for the classes exposed in the public API, without
+// javadoc. This can be used as a starting point for adding a new file to
+// libcore/ojluni/annotations/sdk. See libcore/ojluni/annotations/README.
+droidstubs {
+    name: "openjdk-sdk-stubs-no-javadoc",
+    srcs: [":openjdk_javadoc_files"],
+    installable: false,
+    no_framework_libs: true,
+    args: "--exclude-documentation-from-stubs"
+}
+
+// Generates stub files for the classes exposed in the intra-core or
+// core-platform APIs, without javadoc. This can be used as a starting point
+// for adding a new file to libcore/ojluni/annotations/mmodule.
+// See libcore/ojluni/annotations/README.
+droidstubs {
+    name: "openjdk-mmodule-stubs-no-javadoc",
+    srcs: [
+        ":openjdk_javadoc_files",
+        ":openjdk_mmodule_extra_files",
+    ],
+    installable: false,
+    no_framework_libs: true,
+    args: "--exclude-documentation-from-stubs "
+        + "--hide-annotation libcore.api.Hide ",
+    merge_inclusion_annotations_dirs: ["ojluni-annotated-mmodule-stubs"],
+}