Automatically emit objc_msgSend calls when calling imported or implemented Objective-C methods

- Add intrinsics.objc_super()

- Emit objc_msgSendSuper2 calls when an objc method call is combined with objc_super(self)

- Fix objc_block return value ABI for large struct returns

- Fix objc_implement method wrappers bad ABI for large struct returns and indirect args

- Simplify parameter forwarding for objc_imlpement methods

- Add intrinsics.objc_instancetype to mimi Objective-C instancetype* returns
  This facilitates returning the correct type on subclasses when calling mehtods
  such as `alloc`, `init`, `retain`, etc.

- Refactor Objective-C class implementations generation so that hierarchies are properly initialized

- Better codegen for context passing with ivar-based autocontext

- Allow @superclass on imported objc-c objects

- Better codegen for block forwarding invoker, arguments are forwarded directly

src/entity.cpp

@@ -251,6 +251,8 @@ struct Entity {
 			String  link_name;
 			String  link_prefix;
 			String  link_suffix;
+			String  objc_selector_name;
+			Entity *objc_class;
 			DeferredProcedure deferred_procedure;
 
 			struct GenProcsData *gen_procs;
@@ -266,6 +268,8 @@ struct Entity {
 			bool    is_anonymous               : 1;
 			bool    no_sanitize_address        : 1;
 			bool    no_sanitize_memory         : 1;
+			bool    is_objc_impl_or_import     : 1;
+			bool    is_objc_class_method       : 1;
 		} Procedure;
 		struct {
 			Array<Entity *> entities;