Defer the upgrade scan

Author: Ye Zhu

src/syncHandler.ts

@@ -47,7 +47,7 @@ class SyncHandler implements Disposable {
 
         this.disposables.push(workspace.onDidChangeWorkspaceFolders(() => {
             this.refresh();
-            upgradeManager.scan();
+            setImmediate(() => upgradeManager.scan());  // Deferred
         }));
 
         try {

src/upgrade/upgradeManager.ts

@@ -40,7 +40,8 @@ class UpgradeManager {
             await commands.executeCommand("workbench.view.extension.azureJavaMigrationExplorer");
         }));
 
-        UpgradeManager.scan();
+        // Defer the expensive scan operation to not block extension activation
+        setImmediate(() => UpgradeManager.scan());
     }
 
     public static scan() {