GraphEditor : Fix top level input connection storage and connection logic.

[kwokcb]

Fixes

Fixes: #2815

• Fix setting of interface names on connection
  • Copies logic from commit: PR
  • This is a general logic fix. 09f66bb
• Fix connection renaming setting on input rename. Was not considering nodegraph to upstream connections

Note: Does not fix all related issues but prevents data loss and crashing.

Example:

It is possible to connect a root input to a downstream nodegraph and rename -- in this case the default loaded Marble graph.

<?xml version="1.0"?>
<materialx version="1.39" colorspace="lin_rec709">
  <nodegraph name="NG_marble1">
    <input name="base_color_1" type="color3" uiname="Color 1" uifolder="Marble Color" interfacename="root_input" />
    <!-- Rest of marble... -->
    <output name="out" type="color3" nodename="color_mix" />
  </nodegraph>
  <standard_surface name="SR_marble1" type="surfaceshader">
    <input name="base_color" type="color3" nodegraph="NG_marble1" output="out" />
  </standard_surface>
  <surfacematerial name="Marble_3D" type="material">
    <input name="surfaceshader" type="surfaceshader" nodename="SR_marble1" />
  </surfacematerial>
  <input name="root_input" type="color3" value="0.000303527, 0, 0" />
</materialx>

[kwokcb]

@lfl-eholthouser , @jstone-lucasfilm. This patches enough logic for this workflow to prevent data loss (no connections) / corruption (incorrect connections) / crashing.
It does not fix other outstanding rendering issues.

[kwokcb]

@jstone-lucasfilm . This is the same fix you put in for validation. Would otherwise fail silently leaving Mtlx doc and UiNode graph with different connections.

[kwokcb]

This branch of logic was missing to handle upstream interfaces to nodegraphs.

[kwokcb]

Firewall check if no outputs.