cocoa: Added SDL_HINT_MAC_USE_GCMOUSE.

Reference Issue #16241.

include/SDL3/SDL_hints.h

@@ -2837,6 +2837,26 @@ extern "C" {
  */
 #define SDL_HINT_MAC_SCROLL_MOMENTUM "SDL_MAC_SCROLL_MOMENTUM"
 
+/**
+ * A variable controlling whether the GCMouse API will be used on macOS.
+ *
+ * On supported versions of macOS, GCMouse is usually a better way to
+ * read mouse input, but may cause problems in some scenarios (remote control
+ * software that wants to send non-GCMouse input events, etc).
+ *
+ * When GCMouse is disabled, SDL will use standard Cocoa mouse events.
+ *
+ * The variable can be set to the following values:
+ *
+ * - "0": GCMouse won't be used.
+ * - "1": GCMouse will be used if available. (default)
+ *
+ * This hint needs to be set before SDL_Init().
+ *
+ * \since This hint is available since SDL 3.6.0.
+ */
+#define SDL_HINT_MAC_USE_GCMOUSE "SDL_MAC_USE_GCMOUSE"
+
 /**
  * A variable controlling whether holding down a key will repeat the pressed
  * key or open the accents menu on macOS.

src/video/cocoa/SDL_cocoamouse.m

@@ -451,6 +451,10 @@ static void Cocoa_OnGCMouseDisconnected(GCMouse *mouse)
 
 void Cocoa_InitGCMouse(void)
 {
+    if (!SDL_GetHintBoolean(SDL_HINT_MAC_USE_GCMOUSE, true)) {
+        return;
+    }
+
     @autoreleasepool {
         // These APIs are available starting in macOS Big Sur, but we don't enable
         // GCMouse until Sonoma due to broken motion and button events on MacBooks