Added "firstInput" stat and repurposed the "fileCreatedAt" stat. (#6070)

- The "firstInput" stat is set on first input in game. Used for RTA
  Timing.
- The "fileCreatedAt" stat is now set when then save file is created
  (After the player is done entering the file name). Useful for seeding
  non rando randomizers like Mirrorworld, Enemy Randomizer, extraTraps,
  etc.

soh/include/z64save.h

@@ -97,6 +97,7 @@ typedef struct {
     /*      */ u32 entrancesDiscovered[SAVEFILE_ENTRANCES_DISCOVERED_IDX_COUNT];
     /*      */ u32 scenesDiscovered[SAVEFILE_SCENES_DISCOVERED_IDX_COUNT];
     /*      */ bool rtaTiming;
+    /*      */ uint64_t firstInput;
     /*      */ uint64_t fileCreatedAt;
 } SohStats;