Bug 40091: Load HTTPS Everywhere as a builtin addon in desktop
This loads HTTPS Everywhere as a builtin addon from a hardcoded resource:// URI in desktop. It also ensures that the non-builtin HTTPS Everywhere addon is always uninstalled on browser startup. The reason of making this desktop-only is that there are some issues when installing a builtin extension from geckoview side, making the extension not available on first startup. So, at least for now we handle the Fenix case separately. See #40118 for a followup for investigating these.