qdoc: Resolve macros also for \qmlmodule arguments

Given a macro

macro.QtMinorVersion=12

, it would be nice if qdoc could resolve

\qmlmodule QtQuick 2.\QtMinorVersion

so that the documentation would indeed read

Import Statement:	import QtQuick 2.12

Currently it generates

Import Statement:	import QtQuick 2.\QtMinorVersion

This becomes relevant because, since Qt 5.11, the minor version of almost all QT imports are supposed to reflect the minor version of Qt. Being able to automate (or at least centralize) this would save us from routinely having to touch .qdoc files in quite a few repositories.