ctrl-s does not work for Webview Editor

[tsmaeder]

Bug Description:

Steps to Reproduce:

When I edit a file with the draw.io editor (https://open-vsx.org/extension/hediet/vscode-drawio) ctrl-s has no effect

1. Install the draw.io extension
2. Create a file foo.drawio and open it
3. Add a square figure
4. Observe: the editor tab shows the "unsaved" circle
5. type ctrl-s
6. Observe: the editor tab still shows the "unsaved" circle

My expectation is for ctrl-s to save the editor. It works for text editors.

Additional Information

• Operating System: Windows
• Theia Version: 1.42.0 master

[msujew]

I believe this is a duplicate of #9230. Our implementation of $trySaveDocument uses the EditorManager which doesn't seem to return the custom editor widget when you use getByUri.