Add used qt modules as example tags

As a user, I'd like to look for examples that show usage of a specific Qt module.

As a developer, I don't want to maintain explicit tags in .qdocconf.

To overcome this, we could extend qdoc to extract information about used Qt Modules from the example sources.

Source: CMakeLists.txt file

All examples have a CMakeLists.txt file that lists the dependencies:

find_package(Qt6 REQUIRED COMPONENTS Core Gui Quick QuickControls2)

This could be grepped by qdoc.

Challenge: Some root modules will be all over the place; all examples depend on Core. Also, just because an example uses 'Quick' doesn't mean that it's a good example for development for Quick in itself.

Example tags: Core, Gui, Quick, QuickControls2

Should we 'namespace' this, e.g. to Qt6Core?

Source: QML imports

Many QML Imports don't require a build system dependency. In this case, qdoc could use qmlimportscanner to list all imports.

Example tags: QtQuick, QtQml.Models, QtQuick.Controls, TableModel, Qt.labs.animation