Annotate java.util.Set.

You can see the source files with the annotations in
https://android-review.googlesource.com/c/platform/libcore/+/699804
(which obviously is not intended for submission). The .jaif changes
here were copy-and-pasted from the results of running the
extract-annotations tool on those sources.

Test: make docs
Bug: 64930165
Change-Id: Icdc220fa48285ddf8319e3a901eeea1c71e60709
diff --git a/annotated_java_files.bp b/annotated_java_files.bp
index abde5be..fbb40d9 100644
--- a/annotated_java_files.bp
+++ b/annotated_java_files.bp
@@ -42,5 +42,6 @@
         "ojluni/src/main/java/java/util/Iterator.java",
         "ojluni/src/main/java/java/util/List.java",
         "ojluni/src/main/java/java/util/Map.java",
+        "ojluni/src/main/java/java/util/Set.java",
     ],
 }