qmlls: missing completions on QML module imports

From the original bug report:

import QtQuick.Controls [dot] does not then show the available modules. The old QML Code model does this. It simply offers "as" assuming to then write a namespace.

I think there is a position mismatch and the wrong completion is suggested between
"import QtQuick.Controls." and (whatever root type, "Item" for example). The "as" makes sense after the "Item" (if it were a module), but it does not make sense at the current position.