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

server/tests/imfs.rs

@@ -1,5 +1,5 @@
 use std::{
-    collections::{HashMap, HashSet},
+    collections::{HashMap, HashSet, BTreeSet},
     fs,
     path::PathBuf,
 };
@@ -80,7 +80,7 @@ fn base_tree() -> Result<(TempDir, Imfs, ExpectedImfs, TestResources), Error> {
     expected_roots.insert(root.path().to_path_buf());
 
     let root_item = {
-        let mut children = HashSet::new();
+        let mut children = BTreeSet::new();
         children.insert(foo_path.clone());
         children.insert(bar_path.clone());
 
@@ -91,7 +91,7 @@ fn base_tree() -> Result<(TempDir, Imfs, ExpectedImfs, TestResources), Error> {
     };
 
     let foo_item = {
-        let mut children = HashSet::new();
+        let mut children = BTreeSet::new();
         children.insert(baz_path.clone());
 
         ImfsItem::Directory(ImfsDirectory {
@@ -199,7 +199,7 @@ fn adding_folder() -> Result<(), Error> {
     }
 
     let folder_item = {
-        let mut children = HashSet::new();
+        let mut children = BTreeSet::new();
         children.insert(file1_path.clone());
         children.insert(file2_path.clone());