`shared_ptr<const int>` leads to C++ code that doesn't compile

Expected Behavior

Emit bindings that work. dtolnay/cxx#1006 says that inserting a typedef results in cxx::bridge handling it already. dtolnay/cxx#850 talks about making it easier.

dtolnay/cxx#537 and dtolnay/cxx#885 have some discussions around making this type more useful, but that seems like a secondary problem.

Actual Behavior

C++ code with shared_ptr<const int> produces generated C++ that doesn't compile because it tries using shared_ptr<int>. It looks like bindgen is stripping out the necessary information before autocxx has a chance to do anything about it :(.

Steps to Reproduce the Problem

#800 has a test case with int.

Opaque C++ types might need to be handled differently. My code actually uses absl::Span, which might have other issues that require a hand-written intermediate typedef regardless.

Specifications

• Version: 90c2aa19c131c66ab96d4962157c3afe2c87fcb1
• Platform: Linux

Start with the test case referenced in issue #800, then trace how bindgen represents shared_ptr before autocxx generates C++. Done means the generated bindings preserve the const-qualified pointee and the resulting C++ compiles; check the opaque-type behavior separately.