Entity Tables (EntitySpawnEntry replacement) (#30579)

* Entity table code

* entity table examples

* fix dat shit

* access

* tests tests tests

* sloth review

Content.Shared/EntityTable/EntitySelectors/NoneSelector.cs

@@ -0,0 +1,16 @@
+using Robust.Shared.Prototypes;
+
+namespace Content.Shared.EntityTable.EntitySelectors;
+
+/// <summary>
+/// Selects nothing.
+/// </summary>
+public sealed partial class NoneSelector : EntityTableSelector
+{
+    protected override IEnumerable<EntProtoId> GetSpawnsImplementation(System.Random rand,
+        IEntityManager entMan,
+        IPrototypeManager proto)
+    {
+        yield break;
+    }
+}