SDL_ResetHint() no longer clears the callbacks associated with a hint

Also added SDL_ResetHints() to reset all callbacks, and clarified that SDL_ClearHints() is just used for cleanup at shutdown.

Fixes https://github.com/libsdl-org/SDL/issues/6313

src/dynapi/SDL2.exports

@@ -865,3 +865,4 @@
 ++'_SDL_HasPrimarySelectionText'.'SDL2.dll'.'SDL_HasPrimarySelectionText'
 ++'_SDL_GameControllerGetSensorDataWithTimestamp'.'SDL2.dll'.'SDL_GameControllerGetSensorDataWithTimestamp'
 ++'_SDL_SensorGetDataWithTimestamp'.'SDL2.dll'.'SDL_SensorGetDataWithTimestamp'
+++'_SDL_ResetHints'.'SDL2.dll'.'SDL_ResetHints'

src/dynapi/SDL_dynapi_overrides.h

@@ -891,3 +891,4 @@
 #define SDL_HasPrimarySelectionText SDL_HasPrimarySelectionText_REAL
 #define SDL_GameControllerGetSensorDataWithTimestamp SDL_GameControllerGetSensorDataWithTimestamp_REAL
 #define SDL_SensorGetDataWithTimestamp SDL_SensorGetDataWithTimestamp_REAL
+#define SDL_ResetHints SDL_ResetHints_REAL

src/dynapi/SDL_dynapi_procs.h

@@ -974,3 +974,4 @@ SDL_DYNAPI_PROC(char*,SDL_GetPrimarySelectionText,(void),(),return)
 SDL_DYNAPI_PROC(SDL_bool,SDL_HasPrimarySelectionText,(void),(),return)
 SDL_DYNAPI_PROC(int,SDL_GameControllerGetSensorDataWithTimestamp,(SDL_GameController *a, SDL_SensorType b, Uint64 *c, float *d, int e),(a,b,c,d,e),return)
 SDL_DYNAPI_PROC(int,SDL_SensorGetDataWithTimestamp,(SDL_Sensor *a, Uint64 *b, float *c, int d),(a,b,c,d),return)
+SDL_DYNAPI_PROC(void,SDL_ResetHints,(void),(),)