Define -DQT_NO_FOREACH by default

Almost all KF modules have that set already.

modemmanager-qt and most of the deprecated modules need to opt-out though. I have prepared locally some patches to do that where needed.

There is one small trap due to the enable-condition, which will trigger only once all KF require 5.79. close to the release branching. Though that should be caught by CI then and be a simple fix by adding any still needed remove_definitions(-DQT_NO_FOREACH).