Allow executing npc_pilot_elite NPCs

[NachosChipeados]

Allows players to execute pilot NPCs. Since every mod that uses npc_pilot_elite NPCs for something (see Gruntmode) , also adds similar changes to this, i think it'd be nice to bring this change into Northstar officially.

Before:
https://github.com/user-attachments/assets/489cc6f1-bc9f-4254-88a5-c30c7e30f6d6

After:
https://github.com/user-attachments/assets/b1263242-c6e8-403d-941c-8bed822ef5cc

Also added missing gib + headshot fx, to prevent weirdness.

Before:
https://github.com/user-attachments/assets/d8874ab2-fdeb-48eb-9db8-10526770f717

After:
https://github.com/user-attachments/assets/33eca4fd-3ec4-49a7-805a-024093efd068

HOW TO TEST:

1. Spawn a pilot NPC (ent_create npc_pilot_elite)
2. Try to execute them. Without this pr, you'll just punch them. With this pr, you'll properly execute them as expected.

Know issues:

• If firstperson executions are enabled, the game will create a duplicate pilot ragdoll after the animation's finished. See Firstperson execution issues #885
  https://github.com/user-attachments/assets/68375bb5-29ed-4f59-b5fb-a5eb0a0fcc44

[Alystrasz]

I suspect the PR has side effects.

Without PR

pr_main.webm

With PR

pr_with_main.webm

[NachosChipeados]

I haven't been able to recreate that in my end, so i'm not sure why it happens. Will investigate though

Titanfall.2.2024-10-06.18-12-31.mp4

[NachosChipeados]

Yeah, i've got nothing. This pr doesn't modify their models or animations in any way, and i can't even repoduce the bug locally so i genuinely have no idea what's going on there