Throws on Unsupported caller allocates (and add tests for #344)

In order to add a test for #344 (closed) there was no need to change GI test APIs as gi_marshalling_tests_garray_utf8_full_out_caller_allocated is a good example of what didn't work.

However introspecting that function was also causing a crash, as in general as per issue #106 we don't support most of caller-allocated function subtypes anyways.

This lead to properly handling issues during function arguments caching, as we could end up in a case in which we have initialized the data, but we return early and then we don't know how to de-initialize it.