Cocoa: Fix search path for private Vulkan loader

According to both Apple and LunarG, a private copy of the macOS Vulkan
loader libvulkan.1.dylib should be placed in the Frameworks directory
of the bundle and not its main executable directory.

This commit updates the dynamic loading path accordingly.

Fixes #2113
Closes #2120

src/cocoa_init.m

@@ -460,10 +460,17 @@ void* _glfwLoadLocalVulkanLoaderCocoa(void)
     if (!bundle)
         return NULL;
 
-    CFURLRef url =
-        CFBundleCopyAuxiliaryExecutableURL(bundle, CFSTR("libvulkan.1.dylib"));
+    CFURLRef frameworksUrl = CFBundleCopyPrivateFrameworksURL(bundle);
+    if (!frameworksUrl)
+        return NULL;
+
+    CFURLRef url = CFURLCreateCopyAppendingPathComponent(
+        kCFAllocatorDefault, frameworksUrl, CFSTR("libvulkan.1.dylib"), false);
     if (!url)
+    {
+        CFRelease(frameworksUrl);
         return NULL;
+    }
 
     char path[PATH_MAX];
     void* handle = NULL;
@@ -472,6 +479,7 @@ void* _glfwLoadLocalVulkanLoaderCocoa(void)
         handle = _glfwPlatformLoadModule(path);
 
     CFRelease(url);
+    CFRelease(frameworksUrl);
     return handle;
 }