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/hidapi/SDL_hidapi.c

@@ -29,10 +29,6 @@
  */
 #include "../SDL_internal.h"
 
-#include "SDL_loadso.h"
-#include "SDL_hidapi.h"
-#include "SDL_thread.h"
-#include "SDL_timer.h"
 #include "SDL_hidapi_c.h"
 
 #if !SDL_HIDAPI_DISABLED

src/hidapi/android/hid.cpp

@@ -50,7 +50,6 @@
 
 #if !SDL_HIDAPI_DISABLED
 
-#include "SDL_hints.h"
 #include "../../core/android/SDL_android.h"
 
 #define hid_init                        PLATFORM_hid_init

src/hidapi/ios/hid.m

@@ -22,7 +22,6 @@
 
 #if !SDL_HIDAPI_DISABLED
 
-#include "SDL_hints.h"
 
 #define hid_init                        PLATFORM_hid_init
 #define hid_exit                        PLATFORM_hid_exit

src/hidapi/libusb/hid.c

@@ -29,9 +29,6 @@
 
 #include "../../SDL_internal.h"
 #include "../../thread/SDL_systhread.h"
-#include "SDL_hints.h"
-#include "SDL_mutex.h"
-#include "SDL_thread.h"
 
 #ifdef realloc
 #undef realloc

src/hidapi/linux/hid.c

@@ -22,7 +22,6 @@
 ********************************************************/
 #include "../../SDL_internal.h"
 
-#include "SDL_hints.h"
 
 #ifndef _GNU_SOURCE
 #define _GNU_SOURCE /* needed for wcsdup() before glibc 2.10 */

src/hidapi/mac/hid.c

@@ -21,7 +21,6 @@
  ********************************************************/
 #include "../../SDL_internal.h"
 
-#include "SDL_hints.h"
 
 /* See Apple Technical Note TN2187 for details on IOHidManager. */
 

src/hidapi/windows/hid.c

@@ -21,7 +21,6 @@
 ********************************************************/
 #include "../../SDL_internal.h"
 
-#include "SDL_hints.h"
 
 #include <windows.h>
 
@@ -87,7 +86,6 @@ extern "C" {
 /*#include <stdlib.h>*/
 
 /* SDL C runtime functions */
-#include "SDL_stdinc.h"
 
 #define calloc SDL_calloc
 #define free SDL_free