This PR integrates new response concepts intended for custom companion NPCs, including citizens and other NPCs descending from CNPC_PlayerCompanion. Many of these concepts were ported from Alyx's EP1/EP2 code, but a few of them are completely new.

Here's a list of concepts ported from Alyx:

• TLK_ENEMY_BURNING — Spoken when the NPC's enemy is ignited.
• TLK_DANGER_ZOMBINE_GRENADE — Spoken when a zombine pulls out a grenade.
• TLK_SPOTTED_INCOMING_HEADCRAB — Spoken when an enemy headcrab is seen for the first time while it's already mid-jump.
• TLK_SPOTTED_HEADCRAB_LEAVING_ZOMBIE — Spoken when a headcrab is seen leaving a zombie that just died.
• TLK_SPOTTED_ZOMBIE_WAKEUP — Spoken when a zombie is seen emerging from a slump actbusy.

Alyx is still fully capable of using these concepts.

Here's a list of completely new concepts:

• TLK_TAKING_FIRE — Spoken when someone fires at me, regardless of whether I was hit. (requires ai_shot_notify_targets to be enabled)
• TLK_NEW_ENEMY — Spoken when a new enemy appears. Unlike TLK_STARTCOMBAT, this can be spoken during combat and has no delay between combat engagements. This is intended to be used when a new enemy enters an already-active arena.
• TLK_COMBAT_IDLE — Randomly spoken when in combat, but not currently attacking (e.g. in cover or reloading). Similar to TLK_ATTACKING, but for when in an intermittent combat state.

TLK_TAKING_FIRE uses a new function called OnEnemyRangeAttackedMe which any class descended from CBaseCombatCharacter can use. It's triggered by CBaseEntity::FireBullets() every time it runs. NPCs trigger OnEnemyRangeAttackedMe on their current enemy. Players use a separate function called GetProbableAimTarget to try to determine what the player is most likely aiming at.

This functionality is enabled by a cvar called ai_shot_notify_targets, which is disabled by default. This can be enabled on a mod-by-mod (or map-by-map using game_convar_mod) basis when TLK_TAKING_FIRE is used, or for when the function is used for some other purpose (such as custom AI).

Note that this does not currently account for func_tanks or any other bullets fired by "indirect" entities. It also does not account for non-bullet range attacks.

This PR also adds support for additional enemy and func_tank criteria.

PR Checklist

• My PR follows all guidelines in the CONTRIBUTING.md file
• My PR targets a develop branch OR targets another branch with a specific goal in mind