Avoid multiple submission of work item comment

What does this MR do and why?

Adds a check to prevent cmd-enter from firing >1 comment creation.

MR acceptance checklist

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Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

Before	After

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Open a work item such as a task
2. Add a comment using cmd-enter to submit
3. Quickly hit cmd-enter multiple times
4. Observe that only 1 comment is left

Related to #483640 (closed)