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/core/openbsd/SDL_wscons_kbd.c

@@ -22,11 +22,7 @@
 #include "../../SDL_internal.h"
 #include <dev/wscons/wsksymvar.h>
 #include <dev/wscons/wsksymdef.h>
-#include "SDL_scancode.h"
-#include "SDL_events.h"
-#include "SDL_keyboard.h"
 #include "SDL_wscons.h"
-#include "SDL_log.h"
 #include <sys/time.h>
 #include <dev/wscons/wsconsio.h>
 #include <dev/wscons/wsdisplay_usl_io.h>

src/core/openbsd/SDL_wscons_mouse.c

@@ -20,7 +20,6 @@
 */
 
 #include "../../SDL_internal.h"
-#include "SDL_events.h"
 #include <sys/time.h>
 #include <dev/wscons/wsconsio.h>
 #include <unistd.h>