feat: Add new glfwAddCocoaMTKSubview function

this new function allows glfw to better interface with Apple's metal API.

Before one had to directly interface with the native cocoa window and replace GLFW's content view. Thus removing GLFW's ability to detect input from the window.

Now this function gives user's the ability to add a Metal MTKView as a "subview" which allows the default glfw window view to still capture input while also displaying a Metal view.

README.md

@@ -121,6 +121,7 @@ information on what to include when reporting a bug.
 
 ## Changelog
 
+ - Added `glfwAddCocoaMTKSubview` function for better metal support
  - Added `GLFW_PLATFORM` init hint for runtime platform selection (#1958)
  - Added `GLFW_ANY_PLATFORM`, `GLFW_PLATFORM_WIN32`, `GLFW_PLATFORM_COCOA`,
    `GLFW_PLATFORM_WAYLAND`, `GLFW_PLATFORM_X11` and `GLFW_PLATFORM_NULL` symbols to

include/GLFW/glfw3native.h

@@ -275,6 +275,20 @@ GLFWAPI CGDirectDisplayID glfwGetCocoaMonitor(GLFWmonitor* monitor);
  *  @ingroup native
  */
 GLFWAPI id glfwGetCocoaWindow(GLFWwindow* window);
+
+/*! @brief Adds an 'MTKView' to the window's main NSView as a subview
+ *
+ *
+ *  @errors Possible errors include @ref GLFW_NOT_INITIALIZED.
+ *
+ *  @thread_safety Call this function from the main thread.
+ *
+ *  @since Added in version 3.3.
+ *
+ *  @ingroup native
+ */
+GLFWAPI void glfwAddCocoaMTKSubview(GLFWwindow* window, void* view);
+
 #endif
 
 #if defined(GLFW_EXPOSE_NATIVE_NSGL)

src/cocoa_window.m

@@ -30,6 +30,7 @@
 
 #include <float.h>
 #include <string.h>
+#import <MetalKit/MetalKit.h>
 
 // Returns the style mask corresponding to the window settings
 //
@@ -1950,3 +1951,20 @@ GLFWAPI id glfwGetCocoaWindow(GLFWwindow* handle)
     return window->ns.object;
 }
 
+GLFWAPI void glfwAddCocoaMTKSubview(GLFWwindow* handle, void* view) {
+
+    _GLFWwindow* window = (_GLFWwindow*) handle;
+    _GLFW_REQUIRE_INIT_OR_RETURN();
+
+    if (_glfw.platform.platformID != GLFW_PLATFORM_COCOA)
+    {
+        _glfwInputError(GLFW_PLATFORM_UNAVAILABLE,
+                        "Cocoa: Platform not initialized");
+        return;
+    }
+
+    [window->ns.view addSubview: (MTKView*) view];
+
+
+}
+