gpu,app/internal/wm: add Metal port

The OpenGL (ES) implementations on Apple platforms are deprecated and
don't support GPU compute programs. This change adds support for the
replacement, the Metal GPU API.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

app/internal/wm/os_ios.m

@@ -8,6 +8,8 @@
 #include "_cgo_export.h"
 #include "framework_ios.h"
 
+__attribute__ ((visibility ("hidden"))) Class gio_layerClass(void);
+
 @interface GioView: UIView <UIKeyInput>
 @end
 
@@ -125,6 +127,9 @@ NSArray<UIKeyCommand *> *_keyCommands;
 	gio_onFrameCallback((__bridge CFTypeRef)link);
 }
 
++ (Class)layerClass {
+    return gio_layerClass();
+}
 - (void)willMoveToWindow:(UIWindow *)newWindow {
 	if (self.window != nil) {
 		[[NSNotificationCenter defaultCenter] removeObserver:self
@@ -157,9 +162,6 @@ NSArray<UIKeyCommand *> *_keyCommands;
 	}
 }
 
-- (void)dealloc {
-}
-
 - (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
 	handleTouches(0, self, touches, event);
 }