Amendment does mixins to hanging sign class to make it swing which is very nice, but does not work hanging signs

MehVahdJukaar/amendments#154

There isn't much technical detail there, so I don't see this being our responsibility to fix it.

The argument appears to be that even though we inherit vanilla's sign block entities and use its renderers, that's still not enough for their mixin to apply correctly.

We didn't just use vanilla's sign block entity type because that required hacking into the sign block entity's valid blocks. I think Forge/NeoForge added something later to make this no longer required or easier. However, this was a while ago, so I'm not sure why we did it, but there was definitely a technical reason. I would have loved to make the code simpler if I could have at the time.

I also noticed that the Rats mod, which their mixin appears to specifically support, has the sign work the same way ours do, so maybe the cause is something else?

Anyways, even if our signs not specifically using vanilla's block entity type is the cause, that sounds problematic for compatibility. What if a mod did need to override methods inherited from the sign? That doesn't sound stable.