Replace console.log by LogOutputChannel

Currently, we are using `console.log` but I think we should use [`LogOutputChannel`](https://code.visualstudio.com/api/references/vscode-api#LogOutputChannel) to make it easier to troubleshoot.

`console.log` messages will only show when the developer tools are open.  In contrast, logs sent via `LogOutputChannel` can be viewed directly using the `Developer: Show Logs...` command.

