Cocoa: Use MACH_PORT_NULL for default IOKit port

Looking into the definition of kIOMainPortDefault, the following
description can be found:

When specifying a main port to IOKit functions, the NULL argument
indicates "use the default". This is a synonym for NULL, if you'd
rather use a named constant.

Thus, we do not have to utilize an external symbol for the identifier
of the default main IOKit port, but MACH_PORT_NULL suffice. This
simplifies compatibility between macOS versions as the symbol was
renamed with macOS 12.0.

Fixes #1985
Closes #1994

src/cocoa_monitor.m

@@ -58,7 +58,7 @@ static char* getMonitorName(CGDirectDisplayID displayID, NSScreen* screen)
     io_service_t service;
     CFDictionaryRef info;
 
-    if (IOServiceGetMatchingServices(kIOMainPortDefault,
+    if (IOServiceGetMatchingServices(MACH_PORT_NULL,
                                      IOServiceMatching("IODisplayConnect"),
                                      &it) != 0)
     {
@@ -231,7 +231,7 @@ static double getFallbackRefreshRate(CGDirectDisplayID displayID)
     io_iterator_t it;
     io_service_t service;
 
-    if (IOServiceGetMatchingServices(kIOMainPortDefault,
+    if (IOServiceGetMatchingServices(MACH_PORT_NULL,
                                      IOServiceMatching("IOFramebuffer"),
                                      &it) != 0)
     {

src/cocoa_platform.h

@@ -41,13 +41,6 @@
 typedef void* id;
 #endif
 
-// NOTE: Many Cocoa enum values have been renamed and we need to build across
-//       SDK versions where one is unavailable or the other deprecated
-//       We use the newer names in code and these macros to handle compatibility
-#if MAC_OS_X_VERSION_MAX_ALLOWED < 120000
- #define kIOMainPortDefault kIOMasterPortDefault
-#endif
-
 // NOTE: Many Cocoa enum values have been renamed and we need to build across
 //       SDK versions where one is unavailable or the other deprecated
 //       We use the newer names in code and these macros to handle compatibility