Add missing includes for declaration of pointer types for Qt properties

((Stump branch done in place of old commit))

With Qt6 also for pointer types the full declaration is needed by code generated by moc for QObject properties.

Re: options proposed in the TODO:

Proposing here instead to use the include in the normal source implementation file that also has the explicit moc include for the header (as last year added also across kdevelop sources by kdevelop/kdevelop!459 (merged), see also https://frinring.wordpress.com/2023/06/28/include-also-moc-files-of-headers/). This matches what has been done for non-pointer-types before as well here and there, though usually the source file already included all declarations as otherwise needed for the implementation (which the included moc file amends for all the Qt macros seen in the header).
This in some way matches the second option proposed, just inverted, as we already do include the moc file, just need to also include the missing header there.