Fix variables in chatAgents2 API requests, add tests (#195529)

* Fix variables in chatAgents2 API requests

* Enable file references and the 'used references' section by default in Insiders

* Add integration tests for chat

* Fix equality

* fix test

extensions/vscode-api-tests/package.json

@@ -6,6 +6,8 @@
   "license": "MIT",
   "enabledApiProposals": [
     "authSession",
+    "chatAgents2",
+    "chatVariables",
     "contribViewsRemote",
     "contribStatusBarItems",
     "createFileSystemWatcher",
@@ -20,6 +22,7 @@
     "fileSearchProvider",
     "findTextInFiles",
     "fsChunks",
+    "interactive",
     "mappedEditsProvider",
     "notebookCellExecutionState",
     "notebookDeprecated",
@@ -165,6 +168,12 @@
         ]
       }
     ],
+    "interactiveSession": [
+      {
+        "id": "provider",
+        "label": "Provider"
+      }
+    ],
     "notebooks": [
       {
         "type": "notebookCoreTest",