Use CALayer instead of NSView for EGLNativeWindowType

The only two EGL implementations on macOS are Swiftshader and ANGLE.
While Swiftshader supports both `NSView` and `CALayer` as
`EGLNativeWindowType`, ANGLE supports only `CALayer`. Furthermore
Swiftshader's OpenGL ES frontend is deprecated in favor of using ANGLE's
Vulkan backend on top of Swiftshader's Vulkan frontend.

This means that on macOS `EGLNativeWindowType` should be a `CALayer` for
compatibility with ANGLE.

Fixes #1169.
Closes #1680.

src/cocoa_window.m

@@ -906,6 +906,11 @@ int _glfwPlatformCreateWindow(_GLFWwindow* window,
         }
         else if (ctxconfig->source == GLFW_EGL_CONTEXT_API)
         {
+            // EGL implementation on macOS use CALayer* EGLNativeWindowType so we
+            // need to get the layer for EGL window surface creation.
+            [window->ns.view setWantsLayer:YES];
+            window->ns.layer = [window->ns.view layer];
+
             if (!_glfwInitEGL())
                 return GLFW_FALSE;
             if (!_glfwCreateContextEGL(window, ctxconfig, fbconfig))