chore: update face bounding box landmark calculations

[phantumcode]

Issue #, if available:

Description of changes:

• update the bounding box from landmark calculation based on new algorithm provided by the Rekognition science team.

See similar PR from Liveness JS: aws-amplify/amplify-ui#4685
For reference, documented algorithm in JS

function generateFaceLandamrks(faces, oval_box)
  const keypoints = faces[0].keypoints;
  const face_box_bottom = faces[0].box.yMax;
  const leftEye  =  keypoints[1];
  const rightEye =  keypoints[0];
  const nose    =  keypoints[2];
  const leftEar =  keypoints[5];
  const rightEar =  keypoints[4];

  const ovalHeight = oval_box.yMax- oval_box.yMin;
  const ovalTop = oval_box.yMin;

  const eyeCenter = [];
  eyeCenter[0] = (leftEye[0] + rightEye[0]) / 2;
  eyeCenter[1] = (leftEye[1] + rightEye[1]) / 2;

  const { pupilDistance: pd, faceHeight: fh } =
    getPupilDistanceAndFaceHeight(faces);

  const alpha = 2.0,
    gamma = 1.8;
  const ow = (alpha * pd + gamma * fh) / 2;

  let cx;
  if (eyeCenter[1] <= (ovalTop + ovalHeight) / 2) {
    cx = (eyeCenter[0] + nose[0]) / 2;
  } else {  // when face tilts down
    cx = eyeCenter[0];
  }

  let face_width = ow;
  let face_height = 1.68* face_width;
  let face_box_top = face_box_bottom - face_height;
  let face_box_left = Math.min(cx- ow / 2, rightEar[0]);
  let face_box_right = Math.max(cx+ ow / 2, leftEar[0]);
  
  return {'xMin':face_box_left, 'yMin':face_box_top,  'xMax':face_box_right, 'yMax':face_box_bottom};
}

Check points: (check or cross out if not relevant)

• Added new tests to cover change, if needed
• Build succeeds with all target using Swift Package Manager
• All unit tests pass
• Security oriented best practices and standards are followed (e.g. using input sanitization, principle of least privilege, etc)
• Documentation update for the change if required
• PR title conforms to conventional commit style
• If breaking change, documentation/changelog update with migration instructions

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.