[FEATURE] Support ZDoom Extended Map Nodes

[rakohus]

Is your feature request related to a problem? Please describe.
Increasingly, new projects in the Boom/MBF realm of mapping are using ZDoom Extended Nodes, either compressed or not. In order to play these modern wads, we will need to implement support for this node format.

Describe the solution you'd like to see
Implement support. It is implemented in Crispy Doom and Rum & Raisin Doom. We could look to those ports for a clean implementation.

Additional context
This is currently supported by most of our contemporaries in the source port space: Eternity, PRBoom+, DSDADoom, Woof, Crispy Doom and Rum & Raisin Doom. Information about ZDoom Extended Nodes: https://doomwiki.org/wiki/Node_builder#ZDoom_extended_nodes

[rakohus]

Here is a wad for testing: https://www.dropbox.com/scl/fi/frtklahtwv7icb32yxkkb/Doom-2-In-City-Only-RC6.wad?rlkey=23or1u39j2np4vnt30ogx3507&dl=1

The first few maps use the extended nodes.