fix: Drastically simplifies regions (#1400)

### Summary
- [X] Gets rid of the Dtos
- [X] Simplifies the json serializer registration
- [X] Adds a custom `RegionByName` JsonConverter that can look up other regions that have already been registered.


### BREAKING CHANGE
1. **Child regions must appear after their parents in the JSON file**
2. In the regions json file, _"Parent"_ can no longer be just a string. It must be an object that includes the map.
      - ```json
        "Parent": { "Name": "Britain", "Map": "Felucca" }
        ```

Projects/UOContent/Regions/ExploringDeepCreaturesRegion.cs

@@ -1,8 +1,15 @@
-namespace Server.Regions;
+using System.Text.Json.Serialization;
+
+namespace Server.Regions;
 
 // TODO: Implement
 public class ExploringDeepCreaturesRegion : DungeonRegion
 {
+    [JsonConstructor] // Don't include parent, since it is special
+    public ExploringDeepCreaturesRegion(string name, Map map, int priority, params Rectangle3D[] area) : base(name, map, priority, area)
+    {
+    }
+
     public ExploringDeepCreaturesRegion(string name, Map map, Region parent, params Rectangle3D[] area) : base(name, map, parent, area)
     {
     }