[vscode] Stub vscode 'Notebook' API

[rschnekenbu]

What it does

Stub vscode 'Notebook' API
This enables the possibility to load and start plugins which depend on the 'Notebook' API. The 'Notebook' functionality will not be operational but the rest of the functionality offered by the plugin will be.

Fixes #11786

Contributed on behalf of ST Microelectronics

How to test

1. Install extension GitHub Issue Notebooks from open-vsx, by downloading the vsix file and installing the downloaded file from extension view (note: tested on 0.0.127 on my side).
2. Reproduce the problem in the theia instance before switching to this PR. Try to create a new Github Issues notebook (ctrl+shift+p and type New Github Issue Notebook)
3. An error should be displayed: Activating extension 'GitHub Issue Notebooks' failed: vscode__WEBPACK_IMPORTED_MODULE_0__.workspace.onDidOpenNotebookDocument is not a function
4. Update your theia repository to use this PR
5. Open the same workspace and make sure the message above is no longer displayed when creating a new Github issues notebook. Nothing should happen, as notebook API is only stubbed, not implemented.

Review checklist

• As an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• As a reviewer, I agree to behave in accordance with the review guidelines

[vince-fugnitto]

LGTM 👍 I confirmed that there is no error with the plugin, and the API is correctly marked as stubbed.

I noticed there is no implementation yet for the onNotebook activation event, but given we are only stubbing I think we can keep it for when we actually implement support with #8395.

[vince-fugnitto]

I believe the stubbing of events such as NotebookRendererMessaging.onDidReceiveMessage among others are incorrect and will actually produce errors on activation:

I modified the vscode-github-issues-notebook plugin to make use of the API.

• vscode-github-issue-notebooks-0.0.128.zip

[rschnekenbu]

Thanks @vince-fugnitto! I'll have a look