Port Qt code away from Q_FOREACH/foreach

Port all Qt code away from Q_FOREACH/foreach. According to Lars, this macro was never intended to be used in Qt code, yet it has infiltrated Qt code to a large extent. We can't deprecate it because users have thousands of uses all over the place, but we have QT_NO_FOREACH which can help keep our code base clean.

Porting guide: https://www.kdab.com/goodbye-q_foreach/

Acceptance criteria:

• QT_NO_FOREACH is defined centrally for all Qt code (cf. QT_NO_AS_CONST, QT_NO_QEXCHANGE, ...).
• only test code testing the foreach/Q_FOREACH is #undef'ing QT_NO_FOREACH at the top of the test