Add setNameGlobal which updates connections downstream

[rasmustilljander]

This solves (or partially solves): #1847

This commit adds the method setNameGlobal for Node and NodeGraph. It behaves like setName but also walk downstream and updates corresponding node or nodegraph name.

API added

void Node::setNameGlobal(const std::string& name);
void NodeGraph::setNameGlobal(const std::string& name);

[ld-kerley]

Thanks @rasmustilljander - this looks like it's gonna make editing documents a lot more straight forwards!

[jstone-lucasfilm]

This looks very promising, @rasmustilljander, and I've written up a suggested improvement.

[jstone-lucasfilm]

Great work, @rasmustilljander, and I've written up a proposal for the language of the doc strings.

[jstone-lucasfilm]

For these new docstrings, my recommendation would be to be specific about the element subclass (e.g. Node, NodeGraph), and to omit the repeated language of the general rules for MaterialX element names.

Here's a proposed update to the doc string for the Node method, and the same approach should work for NodeGraph as well:

/// Set the name string of this Node, propagating the updated name to all
/// downstream ports.
/// @throws Exception if an element at the same scope already possesses the
///     given name.

[rasmustilljander]

Looks great, I updated the docs to align with your suggestion!

[jstone-lucasfilm]

This looks good to me, thanks @rasmustilljander!