SDL_rwops read/write functions return size_t again

The current status is stored in the SDL_rwops 'status' field to be able to determine whether a 0 return value is caused by end of file, an error, or a non-blocking source not being ready.

The functions to read sized datatypes now return SDL_bool so you can detect read errors.

Fixes https://github.com/libsdl-org/SDL/issues/6729

include/SDL3/SDL_surface.h

@@ -273,7 +273,8 @@ extern DECLSPEC SDL_Surface *SDLCALL SDL_LoadBMP(const char *file);
  *
  * \param surface the SDL_Surface structure containing the image to be saved
  * \param dst a data stream to save to
- * \param freedst non-zero to close the stream after being written
+ * \param freedst if SDL_TRUE, calls SDL_RWclose() on `dst` before returning,
+ *                even in the case of an error
  * \returns 0 on success or a negative error code on failure; call
  *          SDL_GetError() for more information.
  *
@@ -282,7 +283,7 @@ extern DECLSPEC SDL_Surface *SDLCALL SDL_LoadBMP(const char *file);
  * \sa SDL_LoadBMP_RW
  * \sa SDL_SaveBMP
  */
-extern DECLSPEC int SDLCALL SDL_SaveBMP_RW(SDL_Surface *surface, SDL_RWops *dst, int freedst);
+extern DECLSPEC int SDLCALL SDL_SaveBMP_RW(SDL_Surface *surface, SDL_RWops *dst, SDL_bool freedst);
 
 /**
  * Save a surface to a file.