Allow target path version in a parent module

For example, the QML Engine should be able to locate QtQml.Models 2.x
in both of the following target/installation paths:

• QT_INSTALL_QML/QtQml/Models.2
• QT_INSTALL_QML/QtQml.2/Models

This is required for QtQuick Controls 2. The target path of the module
is QT_INSTALL_QML/QtQuick/Controls.2. The built-in styles are installed
as sub-directories to be able to locate them from the main controls module.

Some of the built-in styles provide their own C++ extensions via style-
specific imports (eg. the Material attached property is imported from
QtQuick.Controls.Material 2.0). The problem is that the QML Engine does
not find the module from QT_INSTALL_QML/QtQuick/Controls.2/Material,
but requires it to be installed outside the main controls module ie.
QT_INSTALL_QML/QtQuick/Controls/Material(.2). This makes it a) hard to
locate the styles from the main controls module, and b) conflicts with
the target path of QtQuick Controls 1.