EmulatorPkg: Change OPTIONAL keyword usage style

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=3760

Update all use of ', OPTIONAL' to ' OPTIONAL,' for function params.

Cc: Andrew Fish <afish@apple.com>
Cc: Leif Lindholm <leif@nuviainc.com>
Cc: Michael Kubacki <michael.kubacki@microsoft.com>
Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com>
Reviewed-by: Ray Ni <ray.ni@intel.com>

EmulatorPkg/Win/Host/WinHost.c

@@ -247,7 +247,7 @@ EfiSystemMemoryRange (
 
 EFI_STATUS
 WinNtOpenFile (
-  IN  CHAR16                    *FileName,            OPTIONAL
+  IN  CHAR16                    *FileName             OPTIONAL,
   IN  UINT32                    MapSize,
   IN  DWORD                     CreationDisposition,
   IN OUT  VOID                  **BaseAddress,