Extensions\GenerateHttpUrl.WinSCPextension.ps1
in WinSCP installation folder.
So typically:
C:\Program Files (x86)\WinSCP\Extensions\GenerateHttpUrl.WinSCPextension.ps1
Though the file gets replaced on each upgrade.
So ideally, you create a copy of the file in your Documents folders and install it to WinSCP.
https://winscp.net/eng/docs/ui_pref_commands#extensions