Auto-reload local workspace extensions when a file in the extension directory gets saved

[TomasHubelbauer]

I am making ample use of the VS Code local workspace extensions feature shipped in v1.89:
https://code.visualstudio.com/updates/v1_89#_local-workspace-extensions

Whenever I make a chance to the extension's source, I have to use the Developer: Reload Window command to make it update.
I think the Reload Extensions button that is in the Extensions pane whenever I install or uninstall extension would also result in the same effect, but that button's underlying action is not exposed as a command that could be found via the command palette AFAIK.

I would like to propose a built-in file save monitor (only when saving a text editor in VS Code not a general file system watcher) that would detect whether the changed file belongs to a directory or a subdirectory of any local workspace extension (extensionPath in the vscode.extensions API) and reload the extension whenever such a file was changed.

I believe something like this could be also crudely done as an extension itself vscode.commands.executeCommand running the workbench.action.restartExtensionHost command based on vscode.workspace.onDidSaveTextDocument with the downside that it could only reload all extensions this way, not any particular one, so I think a built-in solution would be preferred.

[RedCMD]

related: #226511