Investigate removal of the ##NAMESPACE## placeholders from natvis files

The ##NAMESPACE## placeholders in our .natvis.xml files are replaced with the Qt namespace that was specified when configuring Qt (via the -qtnamespace argument).

Problem: a user (who wants the use the natvis files outside of QtVSTools context) can't just take and drop the files somewhere. They have to do this replacement themselves.

Contributors work on the stripped natvis files and would need to re-add the ##NAMESPACE## placeholders when submitting a patch.

It would be nice if we could find some natvis feature that allows us to get rid of this string replacement. Or maybe there's a way to enrich a non-namespaced natvis file with namespaces automatically.

Unfortunately, it doesn't seem like we could drop support for namespaced Qt alltogether.