Cleanup factions code (#11075)

Co-authored-by: Kara <lunarautomaton6@gmail.com>

Content.Server/NPC/Components/FactionComponent.cs

@@ -0,0 +1,29 @@
+using Content.Server.NPC.Systems;
+using Robust.Shared.Serialization.TypeSerializers.Implementations.Custom.Prototype.Set;
+
+namespace Content.Server.NPC.Components
+{
+    [RegisterComponent]
+    [Access(typeof(FactionSystem))]
+    public sealed class FactionComponent : Component
+    {
+        /// <summary>
+        /// Factions this entity is a part of.
+        /// </summary>
+        [ViewVariables(VVAccess.ReadWrite),
+         DataField("factions", customTypeSerializer:typeof(PrototypeIdHashSetSerializer<FactionPrototype>))]
+        public HashSet<string> Factions = new();
+
+        /// <summary>
+        /// Cached friendly factions.
+        /// </summary>
+        [ViewVariables]
+        public readonly HashSet<string> FriendlyFactions = new();
+
+        /// <summary>
+        /// Cached hostile factions.
+        /// </summary>
+        [ViewVariables]
+        public readonly HashSet<string> HostileFactions = new();
+    }
+}