Fix QuatFromXZDirection for negative dx inputs causing ACUs to spawn the wrong direction

[lL1l1]

Issue

Initially reported on Discord that ACUs would sometimes not spawn facing the correct direction after the release with #6438.

This is because the math used in the QuatFromXZDirection(dx, dz) function did not properly account for signs, and was giving the wrong output when dx was negative. ACUs on the right side of the map have a negative dx when rotating towards the middle of the map.

Description of the proposed changes

• Accounts for the sign of -dx
• Explain the mathematics more thoroughly
• Account for the division by zero case as it would print Unit ual0001 is attempting to move to an invalid coord to the log about the unit moving to an invalid coord when SetOrientation({0, 1.#INF, 0, 1.#INF}, true) happened.

Testing done on the proposed changes

• Fill all slots on Crossfire Canal and verify that all ACUs spawn with the correct orientation. Using Crossfire Canal accounts for all quadrants of the unit circle. Make sure to pause the game right after the spawn sequence if using AI, as the AI will move the ACUs.

The follow script tests the differences between the old and new results of RotateTowards, but I didn't bother making the function results exactly the same (there are some switches in sign) because the end result for ACU orientation at the start was fine.

local utilities = import("/lua/utilities.lua")
local oldRotateTowards = function(self, tpos)
    local pos = self.pos
    local rad = math.atan2(tpos[1] - pos[1], tpos[3] - pos[3])
    local function SetRotation(angle)
        local function QuatFromRotation(rotation, x, y, z)
            local angleRot, qw, qx, qy, qz, angle
            angle = 0.00872664625 * rotation
            angleRot = math.sin(angle)
            qw = math.cos(angle)
            qx = x * angleRot
            qy = y * angleRot
            qz = z * angleRot
            return qx, qy, qz, qw
        end
        return QuatFromRotation(angle, 0, 1, 0)
    end
    return SetRotation(rad * (180 / math.pi))
end
LOG(oldRotateTowards({pos = {0, 1, 0}}, {0, 0, 0}))
LOG(repr(utilities.QuatFromXZDirection(0, 0)))

LOG(oldRotateTowards({pos = {0, 1, 0}}, {1, 0, 0}))
LOG(repr(utilities.QuatFromXZDirection(1, 0)))
LOG(oldRotateTowards({pos = {0, 1, 0}}, {0, 0, 1}))
LOG(repr(utilities.QuatFromXZDirection(0, 1)))
LOG(oldRotateTowards({pos = {0, 1, 0}}, {-1, 0, 0}))
LOG(repr(utilities.QuatFromXZDirection(-1, 0)))
LOG(oldRotateTowards({pos = {0, 1, 0}}, {0, 0, -1}))
LOG(repr(utilities.QuatFromXZDirection(0, -1)))

LOG(oldRotateTowards({pos = {0, 1, 0}}, {1, 0, 1}))
LOG(repr(utilities.QuatFromXZDirection(1, 1)))
LOG(oldRotateTowards({pos = {0, 1, 0}}, {1, 0, -1}))
LOG(repr(utilities.QuatFromXZDirection(1, -1)))
LOG(oldRotateTowards({pos = {0, 1, 0}}, {-1, 0, -1}))
LOG(repr(utilities.QuatFromXZDirection(-1, -1)))
LOG(oldRotateTowards({pos = {0, 1, 0}}, {-1, 0, 1}))
LOG(repr(utilities.QuatFromXZDirection(-1, 1)))

Checklist

• Changes are annotated, including comments where useful
• Changes are documented in the changelog for the next game version