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/gl_macos.go

@@ -1,7 +1,7 @@
 // SPDX-License-Identifier: Unlicense OR MIT
 
-//go:build darwin && !ios
-// +build darwin,!ios
+//go:build darwin && !ios && nometal
+// +build darwin,!ios,nometal
 
 package wm