include: Added \threadsafety notes to about 60 more functions.

Reference Issue #7140.

include/SDL3/SDL_init.h

@@ -224,6 +224,8 @@ typedef void (SDLCALL *SDL_AppQuit_func)(void *appstate, SDL_AppResult result);
  * \returns true on success or false on failure; call SDL_GetError() for more
  *          information.
  *
+ * \threadsafety This function should only be called on the main thread.
+ *
  * \since This function is available since SDL 3.2.0.
  *
  * \sa SDL_SetAppMetadata
@@ -244,6 +246,8 @@ extern SDL_DECLSPEC bool SDLCALL SDL_Init(SDL_InitFlags flags);
  * \returns true on success or false on failure; call SDL_GetError() for more
  *          information.
  *
+ * \threadsafety This function should only be called on the main thread.
+ *
  * \since This function is available since SDL 3.2.0.
  *
  * \sa SDL_Init
@@ -260,6 +264,8 @@ extern SDL_DECLSPEC bool SDLCALL SDL_InitSubSystem(SDL_InitFlags flags);
  *
  * \param flags any of the flags used by SDL_Init(); see SDL_Init for details.
  *
+ * \threadsafety This function is not thread safe.
+ *
  * \since This function is available since SDL 3.2.0.
  *
  * \sa SDL_InitSubSystem
@@ -274,6 +280,8 @@ extern SDL_DECLSPEC void SDLCALL SDL_QuitSubSystem(SDL_InitFlags flags);
  * \returns a mask of all initialized subsystems if `flags` is 0, otherwise it
  *          returns the initialization status of the specified subsystems.
  *
+ * \threadsafety This function is not thread safe.
+ *
  * \since This function is available since SDL 3.2.0.
  *
  * \sa SDL_Init
@@ -292,6 +300,8 @@ extern SDL_DECLSPEC SDL_InitFlags SDLCALL SDL_WasInit(SDL_InitFlags flags);
  * application is shutdown, but it is not wise to do this from a library or
  * other dynamically loaded code.
  *
+ * \threadsafety This function should only be called on the main thread.
+ *
  * \since This function is available since SDL 3.2.0.
  *
  * \sa SDL_Init