#1555

This is a very common SDKCall used in plugins and I think it'd be a great idea to have a native for it.

I agree.

Overview

This PR adds two new natives:

// Same as SDKCall to:  int CBaseAnimating::LookupAttachment(const char *)
native int LookupEntityAttachment(int entity, const char[] name);

// Same as SDKCall to:  bool CBaseAnimating::GetAttachment(int, Vector &, QAngle &)
native bool GetEntityAttachment(int entity, int attachment, float origin[3], float angles[3]);

Example usage:

int attachment = LookupEntityAttachment(client, "head");
if (attachment == 0)
	return;

float origin[3], angles[3];
if (!GetEntityAttachment(client, attachment, origin, angles))
	return;

PrintToServer("Attachment %d at: (%f %f %f)", attachment, origin[0], origin[1], origin[2]);

Gamedata for CS:GO, CS:S, L4D, L4D2 and TF2 is provided, but has not been tested by me.

Implementation

Using the virtual CBaseAnimating::GetAttachment(int, matrix3x4_t &) was a deliberate choice because virtual offsets are generally easier to maintain than signatures. The matrix3x4_t is converted to world position and world angles internally.
Some of the other overloads are also inlined on a few games, making this the best choice.

Since this call can only be used on classes inheriting CBaseAnimating, we check if the DT_BaseAnimating SendTable exists on the entity, throwing a native error if it doesn't.
This safeguard could be greatly improved with a call to CBaseEntity::GetBaseAnimating, but would require more gamedata (maybe something to consider for the future?)

Footnote

I have not been able to test this for any game other than TF2. I'd be grateful if other people could assist with testing
this on different games and engine versions.

This is my first time actively working with C++, so excuse some rookie mistakes.