[outline] Symbols added twice under parents when parent name is ambiguous

[MarkZ3]

Using Theia master as of today.

This happens because here the algorithm that figures out which children are under the parent checks only if the parent name matches the candidate child's containerName (both unqualified). So because two parents can have the same unqualified name, a given symbol can be added to two different parents.
microsoft/language-server-protocol#327 would solve this.

[AlexTugarev]

I think there were some changes made recently. Nodes are still added to wrong parent if the name is ambiguous, but no longer twice.