Quaternion to Euler conversion functions

[oldio]

• Added missing quaternion to Euler functions that are currently used by Dots.Animation. Original functions come from core UnityEngine code unity\Runtime\Math\Simd\vec-quat.h:
  • float3 EulerXYZ(quaternion)
  • float3 EulerXZY(quaternion)
  • float3 EulerYXZ(quaternion)
  • float3 EulerYZX(quaternion)
  • float3 EulerZXY(quaternion)
  • float3 EulerZYX(quaternion)
  • float3 Euler(quaternion, RotationOrder)
• Added float math.angle(quaternion q1, quaternion q2) to determine angle between two quaternions
• Fixed nlerp to be branchless
• Fixed quaternion mul to consider sign like core UnityEngine code.
• Added chgsign and it's vector variants in order to change the sign of a value based on the most significant bit of another value.

[unpacklo]

Restoring the branch for @sheredom