Fix HasMenuCurrent and IsDescendant/IsAncestor when comparing to itself

[bep]

Fix HasMenuCurrent and IsDescendant/IsAncestor when comparing to itself

There may be sites in the wild that depends on the faulty behaviour of IsDescendant/IsAncestor when comparing to itself, but

• The documentation and common sense says that a thing cannot be descendant or ancestor to itself.
• The bug introduced in HasMenuCurrent comes directly from that confusion.

Fixes #9846

[bep]

OK, this need some thinking, I notice we already reverted this in #7206 ...

But I don't think we can keep obviously wrong behaviour (which is not in line with the documentation) because it will break some themes. In my head the old behaviour can be had with:

{{ if or (eq $p1 $p2) ($p1.IsAncestor $p2) }}
{{ end }}

/cc @tekezo

[github-actions]

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