Qdoc ignores the excludedirs config for example files list

The Qt for MCUs project config uses the excludedirs config to exclude some of the 3rdparty sources in the demos. Otherwise, the list of example files is too long for some of these demos. Qdoc still lists the project files (CMakeLists.txt, .qrc, .pro, .qmproject, .pyproject, qmldir) in those directories.