QML imports break on UNC paths that contain `%` chars

To reproduce:

• Run app using QML from a network drive and have a `%` somewhere in the path to the executable.

The issue is in `qqmlimport_p.h:401-404`. When the path starts with `//`, `QUrl::toString(QUrl::removeScheme)` is used to convert the URL to string. Unfortunately, this seems to imply `PrettyEncoding` with produces a string with `%25` instead of `%`.

This completely breaks all QML imports. The application will not start properly. It will simply report `module "QtQuick.Window" is not installed` although all DLLs are present.

Please, no questions about running apps from network drives and having `%` in paths. People do.