Add support for declarative type registration in Qbs

https://codereview.qt-project.org/c/qt/qtdeclarative/+/290315/3/src/qml/doc/src/qmlfunctions.qdoc adds support for declaring a QML import in a .pro file in Qt 5.15:

You can use the build system to register the type in the type namespace
"com.mycompany.qmlcomponents" with major version \c 1 by specifying the
following in your project file:

  CONFIG += qmltypes
  QML_IMPORT_NAME = com.mycompany.qmlcomponents
  QML_IMPORT_MAJOR_VERSION = 1

Presumably Qbs will need to support this functionality to allow users to have control over the name of their QML modules.