Switch header convention from #include "SDL.h" to #include <SDL3/SDLh>

I ran this script in the include directory:
```sh
sed -i '' -e 's,#include "\(SDL.*\)",#include <SDL3/\1>,' *.h
```

I ran this script in the src directory:
```sh
for i in ../include/SDL3/SDL*.h
do hdr=$(basename $i)
   if [ x"$(echo $hdr | egrep 'SDL_main|SDL_name|SDL_test|SDL_syswm|SDL_opengl|SDL_egl|SDL_vulkan')" != x ]; then
        find . -type f -exec sed -i '' -e 's,#include "\('$hdr'\)",#include <SDL3/\1>,' {} \;
    else
        find . -type f -exec sed -i '' -e '/#include "'$hdr'"/d' {} \;
    fi
done
```

Fixes https://github.com/libsdl-org/SDL/issues/6575

src/test/SDL_test_assert.c

@@ -24,7 +24,7 @@
  Used by the test framework and test cases.
 
 */
-#include "SDL_test.h"
+#include <SDL3/SDL_test.h>
 
 /* Assert check message format */
 #define SDLTEST_ASSERT_CHECK_FORMAT "Assert '%s': %s"

src/test/SDL_test_common.c

@@ -20,7 +20,7 @@
 */
 
 /* Ported from original test/common.c file. */
-#include "SDL_test.h"
+#include <SDL3/SDL_test.h>
 
 static const char *video_usage[] = {
     "[--video driver]", "[--renderer driver]", "[--gldebug]",

src/test/SDL_test_compare.c

@@ -26,7 +26,7 @@
  Rewritten for test lib by Andreas Schiffler.
 
 */
-#include "SDL_test.h"
+#include <SDL3/SDL_test.h>
 
 
 /* Counter for _CompareSurface calls; used for filename creation when comparisons fail */

src/test/SDL_test_crc32.c

@@ -25,7 +25,7 @@
  Original source code contributed by A. Schiffler for GSOC project.
 
 */
-#include "SDL_test.h"
+#include <SDL3/SDL_test.h>
 
 
 int SDLTest_Crc32Init(SDLTest_Crc32Context *crcContext)

src/test/SDL_test_font.c

@@ -18,7 +18,7 @@
      misrepresented as being the original software.
   3. This notice may not be removed or altered from any source distribution.
 */
-#include "SDL_test.h"
+#include <SDL3/SDL_test.h>
 
 /* ---- 8x8 font definition ---- */
 

src/test/SDL_test_fuzzer.c

@@ -24,7 +24,7 @@
   Data generators for fuzzing test data in a reproducible way.
 
 */
-#include "SDL_test.h"
+#include <SDL3/SDL_test.h>
 
 #include <float.h>      /* Needed for FLT_MAX and DBL_EPSILON */
 #include <limits.h>     /* Needed for UCHAR_MAX, etc. */

src/test/SDL_test_harness.c

@@ -18,7 +18,7 @@
      misrepresented as being the original software.
   3. This notice may not be removed or altered from any source distribution.
 */
-#include "SDL_test.h"
+#include <SDL3/SDL_test.h>
 
 #include <stdlib.h>     /* Needed for exit() */
 

src/test/SDL_test_imageBlit.c

@@ -18,7 +18,7 @@
      misrepresented as being the original software.
   3. This notice may not be removed or altered from any source distribution.
 */
-#include "SDL_test.h"
+#include <SDL3/SDL_test.h>
 
 /* GIMP RGB C-Source image dump (blit.c) */
 

src/test/SDL_test_imageBlitBlend.c

@@ -18,7 +18,7 @@
      misrepresented as being the original software.
   3. This notice may not be removed or altered from any source distribution.
 */
-#include "SDL_test.h"
+#include <SDL3/SDL_test.h>
 
 /* GIMP RGB C-Source image dump (alpha.c) */
 

src/test/SDL_test_imageFace.c

@@ -18,7 +18,7 @@
      misrepresented as being the original software.
   3. This notice may not be removed or altered from any source distribution.
 */
-#include "SDL_test.h"
+#include <SDL3/SDL_test.h>
 
 /* GIMP RGBA C-Source image dump (face.c) */
 

src/test/SDL_test_imagePrimitives.c

@@ -18,7 +18,7 @@
      misrepresented as being the original software.
   3. This notice may not be removed or altered from any source distribution.
 */
-#include "SDL_test.h"
+#include <SDL3/SDL_test.h>
 
 /* GIMP RGB C-Source image dump (primitives.c) */
 

src/test/SDL_test_imagePrimitivesBlend.c

@@ -18,7 +18,7 @@
      misrepresented as being the original software.
   3. This notice may not be removed or altered from any source distribution.
 */
-#include "SDL_test.h"
+#include <SDL3/SDL_test.h>
 
 /* GIMP RGB C-Source image dump (alpha.c) */
 

src/test/SDL_test_log.c

@@ -29,8 +29,7 @@
 #if defined(_MSC_VER) && !defined(_CRT_SECURE_NO_WARNINGS)
 # define _CRT_SECURE_NO_WARNINGS
 #endif
-#include "SDL.h"
-#include "SDL_test.h"
+#include <SDL3/SDL_test.h>
 
 #include <time.h>   /* Needed for localtime() */
 

src/test/SDL_test_md5.c

@@ -50,7 +50,7 @@
  ** documentation and/or software.                                    **
  ***********************************************************************
  */
-#include "SDL_test.h"
+#include <SDL3/SDL_test.h>
 
 /* Forward declaration of static helper function */
 static void SDLTest_Md5Transform(MD5UINT4 * buf, const MD5UINT4 * in);

src/test/SDL_test_memory.c

@@ -18,11 +18,7 @@
      misrepresented as being the original software.
   3. This notice may not be removed or altered from any source distribution.
 */
-#include "SDL_assert.h"
-#include "SDL_stdinc.h"
-#include "SDL_log.h"
-#include "SDL_test_crc32.h"
-#include "SDL_test_memory.h"
+#include <SDL3/SDL_test.h>
 
 #ifdef HAVE_LIBUNWIND_H
 #define UNW_LOCAL_ONLY

src/test/SDL_test_random.c

@@ -27,7 +27,7 @@
  Original source code contributed by A. Schiffler for GSOC project.
 
 */
-#include "SDL_test.h"
+#include <SDL3/SDL_test.h>
 
 #include <stdlib.h>     /* Needed for srand() and rand() */
 #include <time.h>       /* Needed for time() */