Generate bindings for abstract classes.

(But don't generate functions which accept/return by value if a class is abstract. This is only constructors; all other functions can't exist in C++ and therefore won't exist in bindings.)

PiperOrigin-RevId: 468226667
diff --git a/rs_bindings_from_cc/ir.h b/rs_bindings_from_cc/ir.h
index 6327583..cd2e5a8 100644
--- a/rs_bindings_from_cc/ir.h
+++ b/rs_bindings_from_cc/ir.h
@@ -623,6 +623,9 @@
   // * The type is a C++ union, which does not support inheritance
   bool is_inheritable = false;
 
+  // Whether this type is abstract.
+  bool is_abstract = false;
+
   // Whether this `Record` corresponds to a C++ `union`, `struct`, or `class`.
   RecordType record_type;