Entity Tables (EntitySpawnEntry replacement) (#30579)

* Entity table code

* entity table examples

* fix dat shit

* access

* tests tests tests

* sloth review

Content.Shared/EntityTable/EntitySelectors/AllSelector.cs

@@ -0,0 +1,25 @@
+using Robust.Shared.Prototypes;
+
+namespace Content.Shared.EntityTable.EntitySelectors;
+
+/// <summary>
+/// Gets spawns from all of the child selectors
+/// </summary>
+public sealed partial class AllSelector : EntityTableSelector
+{
+    [DataField(required: true)]
+    public List<EntityTableSelector> Children;
+
+    protected override IEnumerable<EntProtoId> GetSpawnsImplementation(System.Random rand,
+        IEntityManager entMan,
+        IPrototypeManager proto)
+    {
+        foreach (var child in Children)
+        {
+            foreach (var spawn in child.GetSpawns(rand, entMan, proto))
+            {
+                yield return spawn;
+            }
+        }
+    }
+}