Introduce InstanceContext (#270)

* Add instance context with dummy field

* Remove stub field

src/snapshot/tests/snapshots/apply__add_property.snap

@@ -1,6 +1,6 @@
 ---
 source: src/snapshot/tests/apply.rs
-expression: tree_value
+expression: tree_view
 ---
 id: id-1
 name: ROOT
@@ -12,4 +12,5 @@ properties:
 metadata:
   ignore_unknown_instances: false
   relevant_paths: []
-children: []
+  context: {}
+children: []

src/snapshot/tests/snapshots/apply__remove_property_after_patch.snap

@@ -1,6 +1,6 @@
 ---
 source: src/snapshot/tests/apply.rs
-expression: tree_value
+expression: tree_view
 ---
 id: id-1
 name: ROOT
@@ -9,4 +9,5 @@ properties: {}
 metadata:
   ignore_unknown_instances: false
   relevant_paths: []
-children: []
+  context: {}
+children: []

src/snapshot/tests/snapshots/apply__remove_property_initial.snap

@@ -1,6 +1,6 @@
 ---
 source: src/snapshot/tests/apply.rs
-expression: tree_value
+expression: tree_view
 ---
 id: id-1
 name: ROOT
@@ -12,4 +12,5 @@ properties:
 metadata:
   ignore_unknown_instances: false
   relevant_paths: []
-children: []
+  context: {}
+children: []

src/snapshot/tests/snapshots/apply__set_name_and_class_name.snap

@@ -1,6 +1,6 @@
 ---
 source: src/snapshot/tests/apply.rs
-expression: tree_value
+expression: tree_view
 ---
 id: id-1
 name: "Hello, world!"
@@ -9,4 +9,5 @@ properties: {}
 metadata:
   ignore_unknown_instances: false
   relevant_paths: []
-children: []
+  context: {}
+children: []

src/snapshot/tests/snapshots/compute__add_child.snap

@@ -10,8 +10,9 @@ added_instances:
       metadata:
         ignore_unknown_instances: false
         relevant_paths: []
+        context: {}
       name: New
       class_name: Folder
       properties: {}
       children: []
-updated_instances: []
+updated_instances: []