Memory leak from BaseType::unify

BaseType::unify returns a pointer to a newly-created Ty on the heap. The caller should be responsible for releasing the memory. As it is, many, many callers are not doing that.

Example of a memory leak(rust-hir-type-check-item.h:58)

    auto result = TypeCheckExpr::Resolve (function.function_body.get (), false);
    auto ret_resolved = expected_ret_tyty->unify (result);   // Memory is allocated here
    if (ret_resolved == nullptr)
      return;

    context->peek_return_type ()->append_reference (ret_resolved->get_ref ());
    context->pop_return_type ();

}   // Pointer goes out of scope here

(Alas, we never worry about such issues in Rust)

Start at BaseType::unify and inspect the example caller at rust-hir-type-check-item.h:58. Trace how the newly allocated Ty is returned and how callers handle it, then identify the other callers that fail to release it. Done means the affected callers no longer leak the memory while preserving the existing unify behavior.