Fix license of VectorImage module

The VectorImage module is currently licensed as Commercial+GPL, but it is documented as part of Qt Quick, so there is no way for users to know the license without actually checking the code.

We either have to re-license the module as LGPL or we need to make it a separate documentation module and make sure it is listed for the correct license. See comments on patch set 10 here: https://codereview.qt-project.org/c/qt/qtdeclarative/+/541966/10