include: A ton of little documentation tweaks, fixes, and improvements.

This is just stuff I noticed while working on the wikiheaders updates. A
thorough pass over all the docs would not be terrible, and maybe a simple
script to check for consistency (does everything have a `\since` on it? etc)
might be nice, too.

include/SDL3/SDL_vulkan.h

@@ -128,7 +128,7 @@ extern DECLSPEC int SDLCALL SDL_Vulkan_LoadLibrary(const char *path);
 extern DECLSPEC SDL_FunctionPointer SDLCALL SDL_Vulkan_GetVkGetInstanceProcAddr(void);
 
 /**
- * Unload the Vulkan library previously loaded by SDL_Vulkan_LoadLibrary()
+ * Unload the Vulkan library previously loaded by SDL_Vulkan_LoadLibrary().
  *
  * \since This function is available since SDL 3.0.0.
  *