Entity Tables (EntitySpawnEntry replacement) (#30579)

* Entity table code

* entity table examples

* fix dat shit

* access

* tests tests tests

* sloth review

Content.Shared/EntityTable/EntitySelectors/NestedSelector.cs

@@ -0,0 +1,20 @@
+using Robust.Shared.Prototypes;
+
+namespace Content.Shared.EntityTable.EntitySelectors;
+
+/// <summary>
+/// Gets the spawns from the entity table prototype specified.
+/// Can be used to reuse common tables.
+/// </summary>
+public sealed partial class NestedSelector : EntityTableSelector
+{
+    [DataField(required: true)]
+    public ProtoId<EntityTablePrototype> TableId;
+
+    protected override IEnumerable<EntProtoId> GetSpawnsImplementation(System.Random rand,
+        IEntityManager entMan,
+        IPrototypeManager proto)
+    {
+        return proto.Index(TableId).Table.GetSpawns(rand, entMan, proto);
+    }
+}