As we may have multiple versions of a QML module present in the
doc build, the logic QDoc uses for merging collection nodes from
different trees needs to be revised a bit.

After this change, the collection nodes for identically-named
QML and JS modules are merged only if the major version number
matches. This prevents the situation where QML types for both
versions are listed in QML module pages.

Change-Id: I76b056a2073744347b160b25ed5bb043279f2b8a
Task-number: QTBUG-47536
Reviewed-by: Martin Smith <martin.smith@digia.com>