Update code to fix Maya API deprecation warnings

[dictoon]

Warnings such as

warning C4996: 'Autodesk::Maya::OpenMaya20190000::MFnDependencyNode::findPlug': Use the MFnDependencyNode::findPlug( const MString&, bool, MStatus* ) method instead.
note: see declaration of 'Autodesk::Maya::OpenMaya20190000::MFnDependencyNode::findPlug'

and

warning C4996: 'Autodesk::Maya::OpenMaya20190000::MFileObject::fullName': Use the methods MFileObject::expandedFullName or MFileObject::resolvedFullName instead.
note: see declaration of 'Autodesk::Maya::OpenMaya20190000::MFileObject::fullName'

There are many more.