[Development] Fixing clazy-fully-qualified-moc-types in Qt sources

[Sze Howe Koh]

I've fixed this warning before [1], but it turns out this is
technically a source-incompatible change [2].

There are also many other instances of violations out there [3] (the
report is 8 years old but many of its results are still valid)

How should we proceed?

(A) Leave them

(B) Fix them (either now or for Qt 7)

(C) (paired with A or B) Add clazy-fully-qualified-moc-types to
https://wiki.qt.io/Things_To_Look_Out_For_In_Reviews#Axivion_/_Clazy_Checks

(D) Make our tools capable of resolving non-fully-qualified types,
thus obsoleting clazy-fully-qualified-moc-types


Regards,
Sze-Howe

[1] https://codereview.qt-project.org/c/qt/qtmultimedia/+/706545
[2] https://codereview.qt-project.org/c/qt/qtremoteobjects/+/706535/comments/4734d24b_e11bffb4
[3] https://docs.kdab.com/analysis/qt5/clazy.html