Adds a HUD icon for crit marines for vampire lurker

[Git-Nivrak]

About the pull request

Adds an HUD icon for marines that can be headbited for vampire This was comically complicated to add

Explain why it's good for the game

Rather than having to spam headbite 20 times until someone is actually unconcious, adds a neat HUD icon.

Testing Photographs and Procedure

Screenshots & Videos

Put screenshots and videos here with an empty line between the screenshots and the <details> tags.

Changelog

:cl: qol: Added an hud icon for vampires that lets them know when an enemy can be executed. /:cl:

[Diegoflores31]

xased

[neeshacark]

vampire lurkers really don't need more handholding, they are already objectively the strongest t2

[github-actions[bot]]

This PR has been inactive for long enough to be automatically marked as stale. This means it is at risk of being auto closed in ~ 7 days, please address any outstanding review items and ensure your PR is finished, if these are all true and you are auto-staled anyway, you need to actively ask maintainers if your PR will be merged. Once you have done any of the previous actions then you should request a maintainer remove the stale label on your PR, to reset the stale timer. If you feel no maintainer will respond in that time, you may wish to close this PR youself, while you seek maintainer comment, as you will then be able to reopen the PR yourself

[Drulikar]

Stale exempt until reviewed again.