Type-specific handle validity checking

[kennykerr]

The win32 metadata now includes information about what constitutes invalid handle values. This update plumbs this through so that you can accurately check whether a handle returned by some function is invalid. Handles will have an is_invalid method if their underlying type is a pointer or have at least one invalid value.

With this information in hand, the bindgen crate can now combine this with metadata that indicates whether a particular function set the last error so that the caller should use GetLastError on failure. This means that functions that return a handle and provide error information in this way will now be transformed to return -> Result<HANDLE> instead of just -> HANDLE. This should make error handling more predictable.

Fixes #1630

[riverar]

Nice! Really cool to see all this light up with a sprinkle of metadata 🎉