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

base/intrinsics/intrinsics.odin

@@ -374,10 +374,11 @@ objc_selector :: struct{}
 objc_class    :: struct{}
 objc_ivar     :: struct{}
 
-objc_id    :: ^objc_object
-objc_SEL   :: ^objc_selector
-objc_Class :: ^objc_class
-objc_Ivar  :: ^objc_ivar
+objc_id           :: ^objc_object
+objc_SEL          :: ^objc_selector
+objc_Class        :: ^objc_class
+objc_Ivar         :: ^objc_ivar
+objc_instancetype :: distinct objc_id
 
 objc_find_selector     :: proc($name: string) -> objc_SEL   ---
 objc_register_selector :: proc($name: string) -> objc_SEL   ---
@@ -385,6 +386,7 @@ objc_find_class        :: proc($name: string) -> objc_Class ---
 objc_register_class    :: proc($name: string) -> objc_Class ---
 objc_ivar_get          :: proc(self: ^$T) -> ^$U ---
 objc_block             :: proc(invoke: $T, ..any) -> ^Objc_Block(T) where type_is_proc(T) ---
+objc_super             :: proc(obj: ^$T) -> ^$U where type_is_subtype_of(T, objc_object) && type_is_subtype_of(U, objc_object) ---
 
 valgrind_client_request :: proc(default: uintptr, request: uintptr, a0, a1, a2, a3, a4: uintptr) -> uintptr ---