Removed SDL as a git submodule

When using Xcode, link with a text based stubbed framework for the library and an external SDL project for the examples.

This prevents downloading multiple copies of SDL when using multiple satellite libraries, and getting conflicts from including multiple copies of SDL projects in your Xcode project.

.gitmodules

@@ -1,7 +1,3 @@
-[submodule "external/SDL"]
-	path = external/SDL
-	url = https://github.com/libsdl-org/SDL.git
-	branch = main
 [submodule "external/jpeg"]
 	path = external/jpeg
 	url = https://github.com/libsdl-org/jpeg.git

Xcode/SDL3.framework/Headers

@@ -0,0 +1 @@
+Versions/Current/Headers

Xcode/SDL3.framework/Resources

@@ -0,0 +1 @@
+Versions/Current/Resources

Xcode/SDL3.framework/SDL3.tbd

@@ -0,0 +1 @@
+Versions/Current/SDL3.tbd

Xcode/SDL3.framework/Versions/A/Headers/SDL.h

@@ -0,0 +1,90 @@
+/*
+  Simple DirectMedia Layer
+  Copyright (C) 1997-2025 Sam Lantinga <[email protected]>
+
+  This software is provided 'as-is', without any express or implied
+  warranty.  In no event will the authors be held liable for any damages
+  arising from the use of this software.
+
+  Permission is granted to anyone to use this software for any purpose,
+  including commercial applications, and to alter it and redistribute it
+  freely, subject to the following restrictions:
+
+  1. The origin of this software must not be misrepresented; you must not
+     claim that you wrote the original software. If you use this software
+     in a product, an acknowledgment in the product documentation would be
+     appreciated but is not required.
+  2. Altered source versions must be plainly marked as such, and must not be
+     misrepresented as being the original software.
+  3. This notice may not be removed or altered from any source distribution.
+*/
+
+/**
+ * Main include header for the SDL library, version 3.2.0
+ *
+ * It is almost always best to include just this one header instead of
+ * picking out individual headers included here. There are exceptions to
+ * this rule--SDL_main.h is special and not included here--but usually
+ * letting SDL.h include the kitchen sink for you is the correct approach.
+ */
+
+#ifndef SDL_h_
+#define SDL_h_
+
+#include <SDL3/SDL_stdinc.h>
+#include <SDL3/SDL_assert.h>
+#include <SDL3/SDL_asyncio.h>
+#include <SDL3/SDL_atomic.h>
+#include <SDL3/SDL_audio.h>
+#include <SDL3/SDL_bits.h>
+#include <SDL3/SDL_blendmode.h>
+#include <SDL3/SDL_camera.h>
+#include <SDL3/SDL_clipboard.h>
+#include <SDL3/SDL_cpuinfo.h>
+#include <SDL3/SDL_dialog.h>
+#include <SDL3/SDL_endian.h>
+#include <SDL3/SDL_error.h>
+#include <SDL3/SDL_events.h>
+#include <SDL3/SDL_filesystem.h>
+#include <SDL3/SDL_gamepad.h>
+#include <SDL3/SDL_gpu.h>
+#include <SDL3/SDL_guid.h>
+#include <SDL3/SDL_haptic.h>
+#include <SDL3/SDL_hidapi.h>
+#include <SDL3/SDL_hints.h>
+#include <SDL3/SDL_init.h>
+#include <SDL3/SDL_iostream.h>
+#include <SDL3/SDL_joystick.h>
+#include <SDL3/SDL_keyboard.h>
+#include <SDL3/SDL_keycode.h>
+#include <SDL3/SDL_loadso.h>
+#include <SDL3/SDL_locale.h>
+#include <SDL3/SDL_log.h>
+#include <SDL3/SDL_messagebox.h>
+#include <SDL3/SDL_metal.h>
+#include <SDL3/SDL_misc.h>
+#include <SDL3/SDL_mouse.h>
+#include <SDL3/SDL_mutex.h>
+#include <SDL3/SDL_pen.h>
+#include <SDL3/SDL_pixels.h>
+#include <SDL3/SDL_platform.h>
+#include <SDL3/SDL_power.h>
+#include <SDL3/SDL_process.h>
+#include <SDL3/SDL_properties.h>
+#include <SDL3/SDL_rect.h>
+#include <SDL3/SDL_render.h>
+#include <SDL3/SDL_scancode.h>
+#include <SDL3/SDL_sensor.h>
+#include <SDL3/SDL_storage.h>
+#include <SDL3/SDL_surface.h>
+#include <SDL3/SDL_system.h>
+#include <SDL3/SDL_thread.h>
+#include <SDL3/SDL_time.h>
+#include <SDL3/SDL_timer.h>
+#include <SDL3/SDL_tray.h>
+#include <SDL3/SDL_touch.h>
+#include <SDL3/SDL_version.h>
+#include <SDL3/SDL_video.h>
+#include <SDL3/SDL_oldnames.h>
+
+#endif /* SDL_h_ */