HL2 player character switching system

[Blixibon]

This PR adds a new "protagonist" system for the HL2 player class and HL2 weapons. This system can be used to switch between preset player models, hand models, and player contexts at ease. These protagonist presets are mounted via a scripts/protagonist_manifest.txt file, which then mounts other files variously formatted like this:

	"BASE_hl2_c_arms"
	{
		"wpn_viewmodels_c"
		{
			"weapon_357"		"models/weapons/hl2_c/v_357.mdl"
			"weapon_ar2"		"models/weapons/hl2_c/v_irifle.mdl"
			"weapon_bugbait"	"models/weapons/hl2_c/v_bugbait.mdl"
			"weapon_crossbow"	"models/weapons/hl2_c/v_crossbow.mdl"
			"weapon_crowbar"	"models/weapons/hl2_c/v_crowbar.mdl"
			"weapon_frag"		"models/weapons/hl2_c/v_grenade.mdl"
			"weapon_physcannon"	"models/weapons/hl2_c/v_physcannon.mdl"
			"weapon_pistol"		"models/weapons/hl2_c/v_pistol.mdl"
			"weapon_rpg"		"models/weapons/hl2_c/v_rpg.mdl"
			"weapon_shotgun"	"models/weapons/hl2_c/v_shotgun.mdl"
			"weapon_slam"		"models/weapons/hl2_c/v_slam.mdl"
			"weapon_smg1"		"models/weapons/hl2_c/v_smg1.mdl"
			"weapon_stunstick"	"models/weapons/hl2_c/v_stunstick.mdl"
		}
	}
	
	//----------------------------------------------------------------------------

	"alyx"
	{
		"inherits_from"		"BASE_hl2_c_arms"
		"playermodel"		"models/alyx.mdl"
		"hands"			"models/weapons/hl2_c/c_arms_alyx.mdl"

		"response_contexts"	"classname:npc_alyx"
	}

	"barney"
	{
		"inherits_from"		"BASE_hl2_c_arms"
		"playermodel"		"models/barney.mdl"
		"hands"			"models/weapons/hl2_c/c_arms_police.mdl"

		"response_contexts"	"classname:npc_barney"
	}

The currently selected protagonist can be selected via a new ProtagonistName keyvalue and a new SetProtagonist input, as well as an equivalent function in VScript.

This PR also adds a new hand_rig weapon script keyvalue which can be used to distinguish between arms-ready viewmodels that were created using different rigs. There are currently only presets for default, css, and blender. Note that this is currently only used by the protagonist system.

---

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

[TeamSpen210]

If the no_suit criteria is only used there, it might be better to use silent_suit or something since it's otherwise fully operational. It's out of scope for this PR and probably a lot of work, but I do wonder if it'd be good to change the suit to instead use response rules. I think you could do the damage diagnosis there with a bunch of rules, allowing complete customisation.

[Blixibon]

If the no_suit criteria is only used there, it might be better to use silent_suit or something since it's otherwise fully operational. It's out of scope for this PR and probably a lot of work, but I do wonder if it'd be good to change the suit to instead use response rules. I think you could do the damage diagnosis there with a bunch of rules, allowing complete customisation.

I agree with making it silent_suit.

I've never considered making the suit use response rules instead. That would require putting the player on CAI_ExpresserHost<>, which I wouldn't be opposed to, but it would open a bunch of other questions and have implications for Mapbase mods which already use responsive players. I'll consider that another time.