Add gmod_wire_customprop

[deltamolfar]

Adds gmod_wire_customprop entity into the wiremod, an entity with custom physics mesh, which isn't spawnable by itself but by the E2/duplicator, and maybe in future, by something else.

It's essentially starfall's custom mesh prop with a few tweaks:

• 16-bit precision vertices positions instead of sf's 32.
• Lower default amount of vertices per convex. As the performance bottleneck of the custom prop is client's ENT:BuildPhysics function, and self:PhysicsInitMultiConvex function in particular which seemingly takes more resources exponentially with the rise of verticies amount, I've decided (and tested by stressing/abusing different limits) to lower the verticies limit and raise convexes limit instead.
• Added convar-controller limit to these props (default is 16), as without it - it's possible to abuse client's performance horribly
• Expression2 functions to spawn said props (+ dynamic cost of creation)

Example of usage: (again, taken mostly from SF's example, not trying to credit myself for other's stuff)

propSpawnUndo(0)

const Fidelity = 15
const X = 150
const Y = 100
const Z = 50

const Convexes = table(
    # cube
    array(
        vec(0, 0, 0), vec(X, 0, 0), vec(X, Y, 0), vec(0, Y, 0),
        vec(0, 0, Z), vec(X, 0, Z), vec(X, Y, Z), vec(0, Y, Z)
    ),
    # cylinder
    array(
        # cone
        vec(X/2, Y/2, Z*3)
    )
)

# cylinder base
for(I = 1, Fidelity) {
    local T = _PI*2 / Fidelity * I
    local Cos = X/2 + cosr(T) * X/4
    local Sin = Y/2 + sinr(T) * Y/4
    
    Convexes[2,array]:pushVector(vec(Cos, Sin, Z))
    Convexes[2,array]:pushVector(vec(Cos, Sin, Z*2))
}

customPropSpawn(Convexes)

[Fasteroid]

I'm in possession of a starfall which spawns an extremely crash-prone level 3 serpinski pyramid (it can crash the server merely by contacting another one of itself).  It has 64 convexes but only 4 verts per convex.  Looks kinda like this:

It might be risky to allow a lot of convexes—the physics mesh isn't costly to build for those but it does cost more to simulate.

Want some help stress-testing this weekend?

[deltamolfar]

Want some help stress-testing this weekend?

Help is always appreciated :)
Regarding the convexes - the default limit it 16 per prop, but if it proves issues, I'm alright with brining it down to 8.