^{Update by Mega_Spud:}
Steps to Reproduce:

1. Go to Settings→Keyboard and Mouse→enable Full Keyboard Gameplay
2. Enter a world
3. Use the directional arrow keys (default) to look around

Observed Results:
The camera movement is slightly jittery / stutters

Expected Results:
The camera movement should be smooth as it moves

Screenshots/Videos attached: Yes

Notes:

Original Description:
When using the smooth camera (from full keyboard gameplay) is no longer smooth at all, and is extremely jittery when looking around.

This use to be actually smooth in 1.12, but since 1.13 its unbearably jittery

Below you can see the controls for smooth camera, and a demo video of it being jittery.
Also note that this is with "rotation speed" set very low. Capturing it on video is a pretty bad representation of this bug, try it out in game your self to see how bad it really is