Inherited methods bindings

[PapyChacal]

This PR offers an implementation for binding inherited methods, using ClassDB::bind_inherited_method<DerivedClass>(...).
It can avoid a lot of boilerplate code in some extensions, where the registered class has to redefine every bound method.
I wasn't sure if this would be helpful on Godot's side or even if it doesn't already work. So tell me if it would be better done there first.

The main obstacle was TYPED_METHOD_BIND in include/godot_cpp/core/method_bind.hpp: it is necessary to call the method on a derived instance to offset this correctly. (Without doing so, the extension compiled but the calls went nuts because this was wrong)

Thus I also offer to get completely rid of TYPED_METHOD_BIND, as in always using typed method bindings. It was introduced in #649 because it was mandatory for Windows builds, but I don't see where not using it would be required: please enlighten me if there is an example.
On top of that, it makes the file much more readable!

[dsnopek]

Thanks!

However, I don't entirely understand why this is necessary? You shouldn't need to bind methods from parent classes again. By virtue of being a child class, the parent methods should all already be bound.

Regarding TYPED_METHOD_BIND: I believe that was added specifically to allow building on MSVC, but (I think) it requires generating more code (ie. the template is instantiated more times for more types). Assuming I have that right, the non-TYPED_METHOD_BIND version allows us to generate smaller binaries when building with GCC or LLVM. So, while all compilers should work fine with the TYPED_METHOD_BIND version, ideally it'd be nice to maintain both.