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/file/SDL_rwops.c

@@ -41,8 +41,6 @@
    data sources.  It can easily be extended to files, memory, etc.
 */
 
-#include "SDL_endian.h"
-#include "SDL_rwops.h"
 
 #ifdef __APPLE__
 #include "cocoa/SDL_rwopsbundlesupport.h"
@@ -54,7 +52,6 @@
 
 #ifdef __ANDROID__
 #include "../core/android/SDL_android.h"
-#include "SDL_system.h"
 #endif
 
 #if defined(__WIN32__) || defined(__GDK__)

src/file/n3ds/SDL_rwopsromfs.c

@@ -20,7 +20,6 @@
 */
 
 #include "SDL_rwopsromfs.h"
-#include "SDL_error.h"
 
 /* Checks if the mode is a kind of reading */
 SDL_FORCE_INLINE SDL_bool IsReadMode(const char *mode);