Experimental/mediapipe pose landmark

[yuhangzheng94]

Update:

• changed the pose recognition model from BlazePose to PoseLandmarker, a new MediaPipe solution in its early release.

Result:

• improved throughput: below 10fps --> ~20fps on Chrome for Yuhang's laptop
• more complete appearance: since all keypoints are predicted even for those out of screen, partial upper body in kiki/bouba mode would show up rather than only showing a line segment

Before	After

New problem:

• poses are constantly jittering

Next steps:

• put smoothPoses() back in place
• look at this discussion: Pose Landmarker Jittering · Issue #4507 · google/mediapipe · GitHub