autocxx: Generate impls for abstract types too

Backport of google/autocxx#1137.

Change-Id: I80e69a93880adf3f907078a55fbdb4e99f15ff2b
Signed-off-by: Brian Silverman <bsilver16384@gmail.com>

third_party/autocxx/engine/src/conversion/codegen_rs/mod.rs

@@ -1042,6 +1042,7 @@ impl<'a> RsCodeGenerator<'a> {
                         extern_c_mod_items: vec![
                             self.generate_cxxbridge_type(name, false, doc_attrs)
                         ],
+                        bridge_items: create_impl_items(&id, movable, destroyable, self.config),
                         bindgen_mod_items,
                         materializations,
                         ..Default::default()

third_party/autocxx/integration-tests/tests/integration_test.rs

@@ -9429,6 +9429,43 @@ fn test_abstract_up() {
     run_test("", hdr, rs, &["A", "get_a"], &[]);
 }
 
+#[test]
+fn test_abstract_up_multiple_bridge() {
+    let hdr = indoc! {"
+    #include <memory>
+    class A {
+    public:
+        virtual void foo() const = 0;
+        virtual ~A() {}
+    };
+    class B : public A {
+    public:
+        void foo() const {}
+    };
+    inline std::unique_ptr<A> get_a() { return std::make_unique<B>(); }
+    "};
+    let hexathorpe = Token![#](Span::call_site());
+    let rs = quote! {
+        autocxx::include_cpp! {
+            #hexathorpe include "input.h"
+            safety!(unsafe_ffi)
+            generate!("A")
+        }
+        autocxx::include_cpp! {
+            #hexathorpe include "input.h"
+            safety!(unsafe_ffi)
+            name!(ffi2)
+            extern_cpp_type!("A", crate::ffi::A)
+            generate!("get_a")
+        }
+        fn main() {
+            let a = ffi2::get_a();
+            a.foo();
+        }
+    };
+    do_run_test_manual("", hdr, rs, None, None).unwrap();
+}
+
 #[test]
 fn test_abstract_private() {
     let hdr = indoc! {"