Insert Model.NeedsPivotMigration in insert_instance when missing (#865)

rojo-test/build-test-snapshots/end_to_end__tests__build__rbxmx_in_folder.snap

@@ -1,7 +1,6 @@
 ---
 source: tests/tests/build.rs
 expression: contents
-
 ---
 <roblox version="4">
   <Item class="Folder" referent="0">
@@ -25,6 +24,7 @@ expression: contents
           <R21>0</R21>
           <R22>1</R22>
         </CoordinateFrame>
+        <bool name="NeedsPivotMigration">false</bool>
         <Ref name="PrimaryPart">null</Ref>
         <BinaryString name="Tags"></BinaryString>
       </Properties>

rojo-test/build-test-snapshots/end_to_end__tests__build__unresolved_values.snap

@@ -1,7 +1,6 @@
 ---
 source: tests/tests/build.rs
 expression: contents
-
 ---
 <roblox version="4">
   <Item class="DataModel" referent="0">
@@ -22,6 +21,7 @@ expression: contents
     <Item class="Workspace" referent="2">
       <Properties>
         <string name="Name">Workspace</string>
+        <bool name="NeedsPivotMigration">false</bool>
       </Properties>
       <Item class="BoolValue" referent="3">
         <Properties>

rojo-test/serve-test-snapshots/end_to_end__tests__serve__empty_json_model_all-2.snap

@@ -1,7 +1,6 @@
 ---
 source: tests/tests/serve.rs
 expression: "read_response.intern_and_redact(&mut redactions, root_id)"
-
 ---
 instances:
   id-2:
@@ -22,7 +21,9 @@ instances:
       ignoreUnknownInstances: false
     Name: test
     Parent: id-2
-    Properties: {}
+    Properties:
+      NeedsPivotMigration:
+        Bool: false
 messageCursor: 1
 sessionId: id-1
 

rojo-test/serve-test-snapshots/end_to_end__tests__serve__empty_json_model_subscribe.snap

@@ -1,7 +1,6 @@
 ---
 source: tests/tests/serve.rs
 expression: "subscribe_response.intern_and_redact(&mut redactions, ())"
-
 ---
 messageCursor: 1
 messages:
@@ -14,7 +13,9 @@ messages:
           ignoreUnknownInstances: false
         Name: test
         Parent: id-2
-        Properties: {}
+        Properties:
+          NeedsPivotMigration:
+            Bool: false
     removed: []
     updated: []
 sessionId: id-1