Add missing docs attributes (#271)

Author: FrancescoC-unity

com.unity.render-pipelines.core/Runtime/Utilities/CoreMatrixUtils.cs

@@ -55,6 +55,7 @@ public static void TranslationTimesMatrix(ref Matrix4x4 inOutMatrix, Vector3 tra
         /// </summary>
         /// <param name="perspective">The perspective matrix to multiply with rhs.</param>
         /// <param name="rhs">A matrix to be multiply to perspective.</param>
+        /// <returns>Returns the matrix that is the result of the multiplication.</returns>
         public static Matrix4x4 MultiplyPerspectiveMatrix(Matrix4x4 perspective, Matrix4x4 rhs)
         {
             Matrix4x4 outMat;
@@ -141,6 +142,7 @@ private static Matrix4x4 MultiplyGenericOrthoMatrix(Matrix4x4 ortho, Matrix4x4 r
         /// <param name="ortho">The ortho matrix to multiply with rhs.</param>
         /// <param name="rhs">A matrix to be multiply to perspective.</param>
         /// <param name="centered">If true, it means that right and left are equivalently distant from center and similarly top/bottom are equivalently distant from center.</param>
+        /// <returns>Returns the matrix that is the result of the multiplication.</returns>
         public static Matrix4x4 MultiplyOrthoMatrix(Matrix4x4 ortho, Matrix4x4 rhs, bool centered)
         {
             return centered ? MultiplyGenericOrthoMatrix(ortho, rhs) : MultiplyOrthoMatrixCentered(ortho, rhs);
@@ -154,6 +156,7 @@ public static Matrix4x4 MultiplyOrthoMatrix(Matrix4x4 ortho, Matrix4x4 rhs, bool
         /// <param name="projMatrix">The projection matrix to multiply with rhs.</param>
         /// <param name="rhs">A matrix to be multiply to perspective.</param>
         /// <param name="orthoCentered">If true, the projection matrix is a centered ( right+left == top+bottom == 0) orthographic projection, otherwise it is a perspective matrix..</param>
+        /// <returns>Returns the matrix that is the result of the multiplication.</returns>
         public static Matrix4x4 MultiplyProjectionMatrix(Matrix4x4 projMatrix, Matrix4x4 rhs, bool orthoCentered)
         {
             return orthoCentered