renderer/metal: properly release texture descriptors

Fixes memory leak. We always need to release these descriptors; the
textures themselves will retain or copy them if necessary.

src/renderer/metal/Target.zig

@@ -68,7 +68,7 @@ pub fn init(opts: Options) !Self {
         const id_init = id_alloc.msgSend(objc.Object, objc.sel("init"), .{});
         break :init id_init;
     };
-    errdefer desc.msgSend(void, objc.sel("release"), .{});
+    defer desc.release();
 
     // Set our properties
     desc.setProperty("width", @as(c_ulong, @intCast(opts.width)));

src/renderer/metal/Texture.zig

@@ -50,7 +50,7 @@ pub fn init(
         const id_init = id_alloc.msgSend(objc.Object, objc.sel("init"), .{});
         break :init id_init;
     };
-    errdefer desc.msgSend(void, objc.sel("release"), .{});
+    defer desc.release();
 
     // Set our properties
     desc.setProperty("pixelFormat", @intFromEnum(opts.pixel_format));