include: Renamed begin_code.h and close_code.h to have SDL_ prefixes.

Fixes #6864.

include/SDL3/SDL_test_memory.h

@@ -30,7 +30,7 @@
 #ifndef SDL_test_memory_h_
 #define SDL_test_memory_h_
 
-#include <SDL3/begin_code.h>
+#include <SDL3/SDL_begin_code.h>
 /* Set up for C function definitions, even when using C++ */
 #ifdef __cplusplus
 extern "C" {
@@ -56,7 +56,7 @@ void SDLTest_LogAllocations(void);
 #ifdef __cplusplus
 }
 #endif
-#include <SDL3/close_code.h>
+#include <SDL3/SDL_close_code.h>
 
 #endif /* SDL_test_memory_h_ */