Actually generate AppliedPatchSet objects (#250)

* Start actually computing AppliedPatchSet values

* Improve patch_apply documentation and flesh out applied patch code

* Add file link notes

* Stub out where tests for snapshot subsystem will go

* Create baseline tests

* Fix build failure by silencing Clippy

src/snapshot/patch.rs

@@ -63,7 +63,7 @@ pub struct PatchUpdate {
 #[derive(Debug, Clone, Default)]
 pub struct AppliedPatchSet {
     pub removed: Vec<RbxId>,
-    pub added: Vec<AppliedPatchAdd>,
+    pub added: Vec<RbxId>,
     pub updated: Vec<AppliedPatchUpdate>,
 }
 
@@ -77,11 +77,6 @@ impl AppliedPatchSet {
     }
 }
 
-#[derive(Debug, Clone)]
-pub struct AppliedPatchAdd {
-    pub instance_id: RbxId,
-}
-
 #[derive(Debug, Clone)]
 pub struct AppliedPatchUpdate {
     pub id: RbxId,
@@ -92,3 +87,15 @@ pub struct AppliedPatchUpdate {
     pub changed_properties: HashMap<String, Option<RbxValue>>,
     pub changed_metadata: Option<InstanceMetadata>,
 }
+
+impl AppliedPatchUpdate {
+    pub fn new(id: RbxId) -> Self {
+        Self {
+            id,
+            changed_name: None,
+            changed_class_name: None,
+            changed_properties: HashMap::new(),
+            changed_metadata: None,
+        }
+    }
+}