Make iOS/tvOS (uikit) SDL_main header-only

Also adjusted iOS demo's includes to <SDL3/..> and explicit SDL_main.h

untested, I don't have Xcode (or a Mac, for that matter)

The xcode projects (for both Xcode-iOS/ and Xcode/) will probably
have to be adjusted for the SDL_main changes to work, but now at least
the iOS demo source should work as is :)

Xcode-iOS/Demos/src/accelerometer.c

@@ -4,7 +4,8 @@
  *  use however you want
  */
 
-#include "SDL.h"
+#include <SDL3/SDL.h>
+#include <SDL3/SDL_main.h>
 #include <math.h>
 #include "common.h"
 

Xcode-iOS/Demos/src/common.c

@@ -5,7 +5,7 @@
  */
 
 #include "common.h"
-#include "SDL.h"
+#include <SDL3/SDL.h>
 #include <stdlib.h>
 
 /*

Xcode-iOS/Demos/src/fireworks.c

@@ -4,8 +4,9 @@
  *  use however you want
  */
 
-#include "SDL.h"
-#include "SDL_opengles.h"
+#include <SDL3/SDL.h>
+#include <SDL3/SDL_main.h>
+#include <SDL3/SDL_opengles.h>
 #include "common.h"
 #include <math.h>
 #include <time.h>

Xcode-iOS/Demos/src/happy.c

@@ -4,7 +4,8 @@
  *  use however you want
  */
 
-#include "SDL.h"
+#include <SDL3/SDL.h>
+#include <SDL3/SDL_main.h>
 #include "common.h"
 
 #define NUM_HAPPY_FACES 100     /* number of faces to draw */

Xcode-iOS/Demos/src/keyboard.c

@@ -4,7 +4,8 @@
  *  use however you want
  */
 
-#include "SDL.h"
+#include <SDL3/SDL.h>
+#include <SDL3/SDL_main.h>
 #include "common.h"
 
 #define TEST_INPUT_RECT

Xcode-iOS/Demos/src/mixer.c

@@ -4,7 +4,8 @@
  *  use however you want
  */
 
-#include "SDL.h"
+#include <SDL3/SDL.h>
+#include <SDL3/SDL_main.h>
 #include "common.h"
 
 #define NUM_CHANNELS 8          /* max number of sounds we can play at once */

Xcode-iOS/Demos/src/rectangles.c

@@ -4,7 +4,8 @@
  *  use however you want
 */
 
-#include "SDL.h"
+#include <SDL3/SDL.h>
+#include <SDL3/SDL_main.h>
 #include <time.h>
 #include "common.h"
 

Xcode-iOS/Demos/src/touch.c

@@ -4,7 +4,8 @@
  *  use however you want
  */
 
-#include "SDL.h"
+#include <SDL3/SDL.h>
+#include <SDL3/SDL_main.h>
 #include <math.h>
 #include "common.h"