dispserv_apple: gate CoreGraphics umbrella and CGDisplayMode APIs

gfx/display_servers/dispserv_apple.m hits two separate SDK cliffs on
pre-10.8 macOS builds:

    dispserv_apple.m:31:38: error:
        CoreGraphics/CoreGraphics.h: No such file or directory

The <CoreGraphics/CoreGraphics.h> umbrella header is 10.8+.  Before
that, the framework is reached through <ApplicationServices/
ApplicationServices.h>.  Swap based on MAC_OS_X_VERSION_MIN_REQUIRED.

The second, latent issue: CGDisplayModeRef and its accessors
(CGDisplayCopyAllDisplayModes, CGDisplayModeGetWidth/Height,
CGDisplaySetDisplayMode) all arrived in 10.6 Snow Leopard.  The 10.5
SDK only exposes the older CGDisplayAvailableModes / CFDictionaryRef
path, which is a different enough shape that porting to both isn't
worth it for a driver whose job is mostly resolution switching.

Introduce RARCH_HAS_CGDISPLAYMODE_API (defined on 10.6+ SDKs) and
gate:

  - get_resolution_list OSX branch (modern path kept; fallback
    reports the current mode as a single entry using the
    pre-10.0 CGDisplayPixelsWide/High APIs)
  - apple_display_server_t.original_mode / display_id fields
  - init block that saves the original display mode
  - destroy block that restores it

apple_display_server_set_resolution needs no change — it was
already gated on __MAC_OS_X_VERSION_MAX_ALLOWED >= 140000 (macOS
14 Sonoma).

Pre-10.6 targets lose resolution-switching but keep window
opacity/progress/decorations.  Modern macOS builds see no change.

gfx/display_servers/dispserv_apple.m

@@ -28,7 +28,29 @@
 
 #ifdef OSX
 #import <AppKit/AppKit.h>
+/* <CoreGraphics/CoreGraphics.h> is a 10.8+ umbrella header.
+ * On earlier SDKs (including the 10.5 Leopard SDK used by Xcode 3.1
+ * on PowerPC), the same types are reachable through the
+ * ApplicationServices umbrella. */
+#include <AvailabilityMacros.h>
+#if defined(MAC_OS_X_VERSION_10_8) && \
+    (!defined(MAC_OS_X_VERSION_MIN_REQUIRED) || \
+     MAC_OS_X_VERSION_MIN_REQUIRED >= MAC_OS_X_VERSION_10_8)
 #import <CoreGraphics/CoreGraphics.h>
+#else
+#import <ApplicationServices/ApplicationServices.h>
+#endif
+/* The CGDisplayModeRef family (CGDisplayCopyAllDisplayModes,
+ * CGDisplayModeGetWidth, CGDisplaySetDisplayMode, ...) arrived in
+ * 10.6 Snow Leopard.  The 10.5 SDK only offers the older
+ * CGDisplayAvailableModes / CFDictionaryRef path, which is a
+ * different enough API that we just stub the resolution list on
+ * pre-10.6 targets rather than port to both. */
+#if defined(MAC_OS_X_VERSION_10_6) && \
+    (!defined(MAC_OS_X_VERSION_MIN_REQUIRED) || \
+     MAC_OS_X_VERSION_MIN_REQUIRED >= MAC_OS_X_VERSION_10_6)
+#define RARCH_HAS_CGDISPLAYMODE_API 1
+#endif
 #endif
 
 #ifdef OSX
@@ -222,6 +244,7 @@ static void *apple_display_server_get_resolution_list(
    double currentRate;
 
 #ifdef OSX
+#ifdef RARCH_HAS_CGDISPLAYMODE_API
    CGDirectDisplayID mainDisplayID = CGMainDisplayID();
    CGDisplayModeRef currentMode = CGDisplayCopyDisplayMode(mainDisplayID);
    currentRate = CGDisplayModeGetRefreshRate(currentMode);
@@ -316,6 +339,33 @@ static void *apple_display_server_get_resolution_list(
    CFRelease(currentMode);
    RARCH_LOG("Found %u display modes on macOS\n", *len);
    return conf;
+#else
+   /* pre-10.6 Leopard/Tiger fallback: CGDisplayModeRef doesn't exist
+    * here and the older CGDisplayAvailableModes API is a different
+    * shape.  Just report the current resolution as a single entry
+    * and skip mode enumeration; resolution-switching isn't supported
+    * on these targets anyway. */
+   CGDirectDisplayID mainDisplayID = CGMainDisplayID();
+   size_t currentWidth             = CGDisplayPixelsWide(mainDisplayID);
+   size_t currentHeight            = CGDisplayPixelsHigh(mainDisplayID);
+
+   *len = 1;
+   if (!(conf = (struct video_display_config*)calloc(1, sizeof(*conf))))
+      return NULL;
+   conf[0].width            = (unsigned)currentWidth;
+   conf[0].height           = (unsigned)currentHeight;
+   conf[0].bpp              = 32;
+   conf[0].refreshrate      = 60;
+   conf[0].refreshrate_float = 60.0f;
+   conf[0].interlaced       = false;
+   conf[0].dblscan          = false;
+   conf[0].idx              = 0;
+   conf[0].current          = true;
+   (void)currentRate;
+   RARCH_LOG("[Video] Legacy macOS: reporting current mode %ux%u only\n",
+         conf[0].width, conf[0].height);
+   return conf;
+#endif /* RARCH_HAS_CGDISPLAYMODE_API */
 #else
    /* iOS/tvOS: Only enumerate refresh rates for current resolution */
    unsigned width, height;
@@ -438,7 +488,7 @@ static enum rotation apple_display_server_get_screen_orientation(void *data)
 
 typedef struct
 {
-#ifdef OSX
+#if defined(OSX) && defined(RARCH_HAS_CGDISPLAYMODE_API)
    CGDisplayModeRef original_mode;
    CGDirectDisplayID display_id;
 #endif
@@ -450,7 +500,7 @@ static void *apple_display_server_init(void)
    if (!apple)
       return NULL;
 
-#ifdef OSX
+#if defined(OSX) && defined(RARCH_HAS_CGDISPLAYMODE_API)
    /* Store original display mode for restoration */
    apple->display_id = CGMainDisplayID();
    apple->original_mode = CGDisplayCopyDisplayMode(apple->display_id);
@@ -503,7 +553,7 @@ static void apple_display_server_destroy(void *data)
    if (!apple)
       return;
 
-#ifdef OSX
+#if defined(OSX) && defined(RARCH_HAS_CGDISPLAYMODE_API)
    /* Restore original display mode */
    if (apple->original_mode)
    {