Renamed SDL_ThreadID() to SDL_GetCurrentThreadID()

Also renamed SDL_threadID to SDL_ThreadID and made it Uint64 for consistency with other ID types

src/thread/ps2/SDL_systhread.c

@@ -98,9 +98,9 @@ void SDL_SYS_SetupThread(const char *name)
     /* Do nothing. */
 }
 
-SDL_threadID SDL_ThreadID(void)
+SDL_ThreadID SDL_GetCurrentThreadID(void)
 {
-    return (SDL_threadID)GetThreadId();
+    return (SDL_ThreadID)GetThreadId();
 }
 
 void SDL_SYS_WaitThread(SDL_Thread *thread)