gpu/headless: move package app/headless

Package headless is more about rendering that windows. Move it
accordingly.

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

gpu/headless/headless_ios.m

@@ -0,0 +1,32 @@
+// SPDX-License-Identifier: Unlicense OR MIT
+
+// +build darwin,ios
+
+@import OpenGLES;
+
+#include <CoreFoundation/CoreFoundation.h>
+#include "_cgo_export.h"
+
+void gio_headless_releaseContext(CFTypeRef ctxRef) {
+	CFBridgingRelease(ctxRef);
+}
+
+CFTypeRef gio_headless_newContext(void) {
+	EAGLContext *ctx = [[EAGLContext alloc] initWithAPI:kEAGLRenderingAPIOpenGLES3];
+	if (ctx == nil) {
+		return nil;
+	}
+	return CFBridgingRetain(ctx);
+}
+
+void gio_headless_clearCurrentContext(CFTypeRef ctxRef) {
+	[EAGLContext setCurrentContext:nil];
+}
+
+void gio_headless_makeCurrentContext(CFTypeRef ctxRef) {
+	EAGLContext *ctx = (__bridge EAGLContext *)ctxRef;
+	[EAGLContext setCurrentContext:ctx];
+}
+
+void gio_headless_prepareContext(CFTypeRef ctxRef) {
+}