Adds flush option to Reagent Pouch Autoinjectors

[halgmor]

About the pull request

Adds a flush option to the Reagent Pouch Autoinjectors.

Explain why it's good for the game

You currently can flush pouch containers, but not the injectors. Meaning, after flushing your container, your injector is STILL filled with reagents that you had wanted cleared out, yet they're stuck in it with no way out other than injecting them into yourself and hope you don't OD.

Testing Photographs and Procedure

Screenshots & Videos

Changelog

🆑
qol: Reagent Pouch Autoinjectors can now be flushed.
/:cl:

[Puckaboo2]

I already have this covered in #11357.

[Drulikar]

Also is there any reason you'd prefer this being done on /obj/item/reagent_container/hypospray/autoinjector/empty/medic instead of /obj/item/reagent_container/hypospray/autoinjector/empty like in Puck's PR? If not then the PR is probably moot.

[halgmor]

Also is there any reason you'd prefer this being done on /obj/item/reagent_container/hypospray/autoinjector/empty/medic instead of /obj/item/reagent_container/hypospray/autoinjector/empty like in Puck's PR? If not then the PR is probably moot.

Yes, several reasons:

1. I wanted to address medics' autoinjectors specifically and especially because of accidental cross-contamination during multiple autoinjector juggling in the field.
   Your half-full custom mix autoinjector was accidentally added to the second pouch that contains another custom mix. Your autoinjector is now full with both mixes together and you cannot "examine" the reagents within the autoinjector nor can you know what the marine patient has in their system while marines are dying around you and xenos are coming down on your head. You would need to flush the autoinjector and refill, but currently you can't do that. This PR gives you that option.
   Another scenario would be in the medical prep room, you fill the pouch with a mix, add the wrong autoinjector to it, now you have 15u of unknown chems that you need to offload into someone to refill the autoinjector, and then you still need to refill the pouch back to 480.

2. I wanted a tighter, targeted, more limited scope with less chance of unintended consequences

3. A smaller change I believed would provide a more digestible PR with a quicker turnaround time and therefore faster relief for medics and their Reagent Pouch Autoinjectors than implementing a wider change

4. Puck's PR, I imagine, will take a good while before it's out. Comparably, this tiny PR will provide immediate relief for medics without having to wait for a larger PR to be tested, reworked, refined, and dragged through weeks/months of revisions and changes