title: Unity shader (hlsl) equivalent of Vector3.ProjectOnPlane
body: <p>In a shader for Unity (hlsl) I'm looking for a way to project a vector(float3 or float4) onto a plane given the plane's normal direction.  What I need is something equivalent to Unity's Vector3.ProjectOnPlane function:
  <a href="https://docs.unity3d.com/ScriptReference/Vector3.ProjectOnPlane.html" rel="nofollow noreferrer">https://docs.unity3d.com/ScriptReference/Vector3.ProjectOnPlane.html</a></p>