C#/Mono: Check assembly version when loading

Not sure if we should check revision too, but this is good enough for what we want.
This will be needed to load the correct Microsoft.Build when we switch to the nuget version.

modules/mono/managed_callable.cpp

@@ -82,6 +82,7 @@ CallableCustom::CompareLessFunc ManagedCallable::get_compare_less_func() const {
 }
 
 ObjectID ManagedCallable::get_object() const {
+	// TODO: If the delegate target extends Godot.Object, use that instead!
 	return CSharpLanguage::get_singleton()->get_managed_callable_middleman()->get_instance_id();
 }