Move GetModuleName to Common

This unifies GetModuleFileName calls between Dolphin and WinUpdater
and allows to gracefully remove MAX_PATH limit from GetExePath

Source/Core/Common/CommonFuncs.h

@@ -4,6 +4,7 @@
 
 #pragma once
 
+#include <optional>
 #include <string>
 #include "Common/CommonTypes.h"
 
@@ -47,4 +48,7 @@ std::string LastStrerrorString();
 // Wrapper function to get GetLastError() string.
 // This function might change the error code.
 std::string GetLastErrorString();
+
+// Obtains a full path to the specified module.
+std::optional<std::wstring> GetModuleName(void* hInstance);
 #endif