The webview only leaves its initial loading screen once it receives a
connectionStatus=connected postMessage. VS Code drops postMessage calls made
before the webview's acquireVsCodeApi bridge is ready, so on slow/remote
networks the single send in _sendCachedState() can be lost forever, leaving
the sidebar stuck on #initial-loading.
Re-send connectionStatus at staggered delays (0.5s-20s) when connected, in
ChatViewProvider, AgentManagerPanelProvider and SessionEditorPanelProvider.
Stops automatically when the view/panel is disposed or replaced. Message is
idempotent.
Fixes#2996
vinciyan
0e39cfb79a