New snapshot tests (#134)

* Changes project-related structures to use `BTreeMap` instead of `HashMap` for children to aid determiniusm
* Changes imfs-related structures to have total ordering and use `BTreeSet` instead of `HashSet`
* Upgrades dependencies to `bx_dom_weak`1.2.0 and rbx_xml 0.5.0 to aid in more determinism stuff
* Re-exposes the `RbxSession`'s root project via `root_project()`
* Implements `Default` for a couple things
* Tweaks visualization code to support visualizing trees not attached to an `RbxSession`
* Adds an ID-invariant comparison method for `rbx_tree` relying on previous determinism changes
* Adds a (disabled) test to start finding issues in the reconciler with regards to communicativity of snapshot application
* Adds a snapshot testing system that operates on `RbxTree` and associated metadata, which are committed in this change

test-projects/multi_partition_game/default.project.json

@@ -0,0 +1,21 @@
+{
+  "name": "multi_partition_game",
+  "tree": {
+    "$className": "DataModel",
+    "ReplicatedStorage": {
+      "$className": "ReplicatedStorage",
+      "Ack": {
+        "$path": "a"
+      },
+      "Bar": {
+        "$path": "b"
+      }
+    },
+    "HttpService": {
+      "$className": "HttpService",
+      "$properties": {
+        "HttpEnabled": true
+      }
+    }
+  }
+}