Improve porting guide to show how to port from Qt Graphical Effects

Graphical Effects look very different in Qt 6 compared to Qt 5: https://www.qt.io/blog/a-short-guide-to-qt-quick-effects However, information on how to port is scattered.

• https://doc.qt.io/qt-6/portingguide.html#check-the-changes-to-the-modules points to https://doc.qt.io/qt-6/whatsnew60.html#removed-modules-in-qt-6-0 which is now an outdated snapshot of Qt 6.0. It only says that "Qt Graphical Effects" is replaced by "Qt 5 Compatibility APIs: Graphical Effects", but the better alternatives are not mentioned.

• https://doc.qt.io/qt-6/qtgraphicaleffects5-index.html has a short note pointing to MultiEffect and Qt Quick Effect Maker (QQEM), but:
  • QQEM should be hyperlinked.
  • Other alternatives are not mentioned.

Suggestions

1. For every 6.0/6.1/6.2 specific page under https://doc.qt.io/qt-6/portingguide.html#check-the-changes-to-the-modules the up-to-date  version of that page should be merged into https://doc.qt.io/qt-6/modulechanges.html
2. The merged section about "Qt Graphical Effects" should point to all available Effects technologies (and ideally an overview on how to choose between them - see the blog post above)
3. https://doc.qt.io/qt-6/portingguide.html#check-the-changes-to-the-modules should point to the up-to-date https://doc.qt.io/qt-6/modulechanges.html, and the 6.0/6.1/6.2 specific links should disappear
4. https://doc.qt.io/qt-6/qtgraphicaleffects5-index.html should point to the new, consolidated information above

(These suggestions are focused on Qt Graphical Effects, but all other modules would benefit too)