Prepare & adapt includes to no <QtDBus> include being used in deps

QStringBuilder is being explicitly included to match the old state where <QtDBus> also pulls in <QtCore> which again pulls in <QStringBuilder> without condition, other than <QString> which only does when either QT_USE_FAST_OPERATOR_PLUS or QT_USE_QSTRINGBUILDER is set, which is not the case currently for plasma-nm. The use of operator% for string concatenation in the respective files though needs <QStringBuilder> being included as it is defined there, so it has to be done explicitly now (until plasma-nm is changed to use QT_USE_QSTRINGBUILDER).

Patch done to prepare for remove of <QtDBus> usage in 2 deps: frameworks/modemmanager-qt!26 (merged) & frameworks/networkmanager-qt!41 (merged)