Made module_local types take precedence over global types

Attempting to mix py::module_local and non-module_local classes results
in some unexpected/undesirable behaviour:

- if a class is registered non-local by some other module, a later
  attempt to register it locally fails.  It doesn't need to: it is
  perfectly acceptable for the local registration to simply override
  the external global registration.
- going the other way (i.e. module `A` registers a type `T` locally,
  then `B` registers the same type `T` globally) causes a more serious
  issue: `A.T`'s constructors no longer work because the `self` argument
  gets converted to a `B.T`, which then fails to resolve.

Changing the cast precedence to prefer local over global fixes this and
makes it work more consistently, regardless of module load order.

tests/test_local_bindings.cpp

@@ -57,6 +57,18 @@ TEST_SUBMODULE(local_bindings, m) {
     py::bind_vector<std::vector<NonLocal2>>(m, "LocalVec2", py::module_local());
     py::bind_map<std::unordered_map<std::string, uint8_t>>(m, "NonLocalMap2", py::module_local(false));
 
+    // test_mixed_local_global
+    // We try this both with the global type registered first and vice versa (the order shouldn't
+    // matter).
+    m.def("register_mixed_global", [m]() {
+        bind_local<MixedGlobalLocal, 100>(m, "MixedGlobalLocal", py::module_local(false));
+    });
+    m.def("register_mixed_local", [m]() {
+        bind_local<MixedLocalGlobal, 1000>(m, "MixedLocalGlobal", py::module_local());
+    });
+    m.def("get_mixed_gl", [](int i) { return MixedGlobalLocal(i); });
+    m.def("get_mixed_lg", [](int i) { return MixedLocalGlobal(i); });
+
     // test_internal_locals_differ
     m.def("local_cpp_types_addr", []() { return (uintptr_t) &py::detail::registered_local_types_cpp(); });
 }