Fix snippet codes for Qt Quick and Qt QML

Fix the snippet codes in Qt Quick and Qt QML.

Things to look for:
-make sure that in the qdocconf files (src/qml/doc/ and src/quick/doc), exampledirs are pointing to the ../../../example and the snippet directory
-make sure that the \snippet command uses the exampledir as the base path. so instead of "\snippet examples/declarative/../file.cpp", use "\snippet file.cpp"
-build locally and reduce the QDoc errors

If possible, run the snippet code.