[User experience] Invoke completion when adding comments using shortcut keys.

## Description

The completion was invoked when I type `/` twice, but it can not invoke when I type `command` + `/` (or `ctrl` + `/` on Windows) as shortcut keys for `// `, like the demo gif below.


## Wanted

The completion when I type `command` + `/`.

: )

Start by reproducing the behavior in the VS Code extension with `/` twice and with Command+/ or Ctrl+/ while adding a comment. Trace the extension's completion and shortcut-key entry points, then verify that the same completion appears for both shortcut variants without breaking the existing trigger.

Written by the indexing model from the issue text.