Move restore flag behind feature flag. Whitelist restorable tabs in for Fabric. Restore e2e tests.

src/Platform/Hosted/extractFeatures.ts

@@ -38,6 +38,7 @@ export type Features = {
   readonly copilotChatFixedMonacoEditorHeight: boolean;
   readonly enablePriorityBasedExecution: boolean;
   readonly disableConnectionStringLogin: boolean;
+  readonly restoreTabs: boolean;
 
   // can be set via both flight and feature flag
   autoscaleDefault: boolean;
@@ -108,6 +109,7 @@ export function extractFeatures(given = new URLSearchParams(window.location.sear
     copilotChatFixedMonacoEditorHeight: "true" === get("copilotchatfixedmonacoeditorheight"),
     enablePriorityBasedExecution: "true" === get("enableprioritybasedexecution"),
     disableConnectionStringLogin: "true" === get("disableconnectionstringlogin"),
+    restoreTabs: "true" === get("restoretabs"),
   };
 }