Add AI factions (#1807)

* Add NPC faction tags

Some stuff isn't easy to represent by the existence of components so tags are intended to provide that functionality for AI usage.

I was 50/50 on having all tags in the 1 component or splitting it into 2. I'm leaning towards 2. This would be for stuff like say "CanMimic" so the mimic knows it's allowed to look like a specific prototype, or something like "smg" on a gun so it can say smg-specific barks for instance (as currently smgs and pistols look the same from a component perspective).

This also means combat behaviors aren't hardcoded per faction, plus it makes it easy to update faction relations during events.

* Factions command

Update faction relationships via commands.

* Remove command TODO

* Woops

Forgot to commit these items

* Serializer writing and parsing

* linq me up fam

Co-authored-by: Metal Gear Sloth <metalgearsloth@gmail.com>

Content.Server/GameObjects/Components/AI/AiFactionTagComponent.cs

@@ -0,0 +1,49 @@
+using System;
+using System.Collections.Generic;
+using Robust.Shared.GameObjects;
+using Robust.Shared.Serialization;
+
+namespace Content.Server.GameObjects.Components.AI
+{
+    [RegisterComponent]
+    public sealed class AiFactionTagComponent : Component
+    {
+        public override string Name => "AiFactionTag";
+
+        public Faction Factions { get; private set; } = Faction.None;
+
+        public override void ExposeData(ObjectSerializer serializer)
+        {
+            base.ExposeData(serializer);
+            
+            serializer.DataReadWriteFunction(
+                "factions",
+                new List<Faction>(),
+                factions => factions.ForEach(faction => Factions |= faction),
+                () =>
+                {
+                    var writeFactions = new List<Faction>();
+                    foreach (Faction fac in Enum.GetValues(typeof(Faction)))
+                    {
+                        if ((Factions & fac) != 0)
+                        {
+                            writeFactions.Add(fac);
+                        }
+                    }
+
+                    return writeFactions;
+                });
+        }
+    }
+
+    [Flags]
+    public enum Faction
+    {
+        None = 0,
+        NanoTransen = 1 << 0,
+        SimpleHostile = 1 << 1,
+        SimpleNeutral = 1 << 2,
+        Syndicate = 1 << 3,
+        Xeno = 1 << 4,
+    }
+}