Vertical knockback is unaffected by knockback resistance

Partner Rank: 3

Verification builds: 1.16.100.59, 1.16.200
Regression builds: None, this always existed

Summary: Knockback resistance only dampens horizontal knockback. Vertical knockback is always the same unless knockback resistance is 100%.

Impact: We have an upcoming map with combat mechanics that are made worse/less fun by this behavior.

Repro Steps:

1. Download and open the attached world
2. Punch the cow on the left that has 100% knockback resistance
3. Punch the cow on the right that has 99.9% knockback resistance

Expected Results: Practically no difference

Observed Results: The cow on the right is knocked a whole block vertically into the air

Screenshots/Videos attached: Yes