[Telemetry] Discard empty suggestions
Problem
Currently, if a code suggestion comes back empty (no choices to display) we rightfully don't display anything to the user. However, in this case we still send a show
event for the suggestion although nothing get's displayed. See https://gitlab.com/gitlab-org/gitlab-vscode-extension/-/blob/1f4efd506febad983f371495a181e17bb63eaf5e/src/common/code_suggestions/code_suggestions_provider.ts#L328
Desired Outcome
suggestion_shown
event is only fired when a suggestion is actually displayed to the user.
Potential solution
Move the event closer to when the "showing" of the suggestion happens.