Makes default the j2objc flags (--nullability and --class-properties) that improve Swift importing. j2objc now has --no-nullability and --no-class-properties flags for teams that don't want this default.

PiperOrigin-RevId: 303524660
diff --git a/src/main/java/com/google/devtools/build/lib/rules/objc/J2ObjcConfiguration.java b/src/main/java/com/google/devtools/build/lib/rules/objc/J2ObjcConfiguration.java
index 086bfa1..64c59d0 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/objc/J2ObjcConfiguration.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/objc/J2ObjcConfiguration.java
@@ -54,7 +54,7 @@
    * See http://j2objc.org/docs/j2objc.html for flag documentation.
    */
   private static final ImmutableList<String> J2OBJC_DEFAULT_TRANSLATION_FLAGS =
-      ImmutableList.of("-g");
+      ImmutableList.of("-g", "--nullability", "--class-properties");
 
   /**
    * Disallowed flags for J2ObjC translation. See http://j2objc.org/docs/j2objc.html for flag