Leave out children already shown in ancestor node

[HebaruSan]

Problem

Many mod relationships are mutual/circular, so mod X conflicts with Y, and Y also conflicts with X.

In the 1.24 pre-release version of the GUI relationships tab, this means you can expand them in an infinite chain if you want to, back and forth forever. This causes visual clutter and is a bit silly looking. Example from #2257:

Changes

Now we omit the children of nodes that already have their children shown as part of their own ancestry. The user will have seen them already when they expanded the identical ancestor node.

This is done by walking the tree via TreeNode.Parent up to the root and comparing the CkanModule objects located in the .Tag property.

Fixes #2257.

[politas]

Would it not make sense to just check whether a mod already appears as an expanded treenode and refuse to expand it (showing an "Already expanded" fake node as the only child)? That would prevent loops of three or more mods as well.

[HebaruSan]

This solution handles loops of three or more mods. It checks all of the ancestor nodes.

"already appears as an expanded treenode" sounds like it would be path-dependent; whether or not you see a relationship would depend on what other nodes you've expanded previously. I think it's better to use something consistent.

[politas]

Ah, ok, I must have misread your description.

As for the path-dependant expansion; it's how a tool I have at work handles expansion of related objects. It's not important.