[REPL Window] Make opening the REPL window on connect async

[cfehse]

The opening of the REPL window during the connect sequence should be done asynchronously to avoid blocking of the connection process if the REPL window cannot be loaded or initialized. In such a case the connection could be established even if the REPL window is not working.

Background for this may be vscode errors like these:

• asWebviewUri: UriError - the path cannot begin with two slash characters
• Webview.asWebviewUri not working in Remote