Common: update Quaternion to allow rotating pitch, yaw, and roll all at once

Source/Core/Common/Matrix.cpp

@@ -56,6 +56,13 @@ Quaternion Quaternion::RotateZ(float rad)
   return Rotate(rad, Vec3(0, 0, 1));
 }
 
+Quaternion Quaternion::RotateXYZ(const Vec3& rads)
+{
+  const auto length = rads.Length();
+  return length ? Common::Quaternion::Rotate(length, rads / length) :
+                  Common::Quaternion::Identity();
+}
+
 Quaternion Quaternion::Rotate(float rad, const Vec3& axis)
 {
   const auto sin_angle_2 = std::sin(rad / 2);

Source/Core/Common/Matrix.h

@@ -337,6 +337,10 @@ public:
   static Quaternion RotateY(float rad);
   static Quaternion RotateZ(float rad);
 
+  // Returns a quaternion with rotations about each axis simulatenously (e.g processing gyroscope
+  // input)
+  static Quaternion RotateXYZ(const Vec3& rads);
+
   static Quaternion Rotate(float rad, const Vec3& axis);
 
   Quaternion() = default;