Implement changing working folder in RD WebIDE

Problem

When accessing Workspace through WebIDE, it's currently impossible to change the working folder in VS Code.

WebIDE	WebUI (built-in to the server)
open-folder-web-ide	open-folder-web-ui

This is caused by the WebIDE sandboxing the VS Code UI in an iframe. By default VS Code tries to change the URL in the window.location to reflect the new folder. This can't be done from the iframe.

Proposed solution

Implement a mechanism that doesn't rely on window.location (URL) to change VS Code working folder path.

More details

• This issue has been first discovered here #368980 (comment 1070204630)
• Paul suggested a solution in this comment: #368980 (comment 1042375777)
• I use the term working folder for VS Code workspace folder, trying to avoid the confusion with our term Workspace