On old worlds fallDamage is set to false by default

On old worlds fallDamage is set to false by default.

What I expected to happen was...:

fallDamage should be set to false by default.

What actually happened was...:
fallDamage was set to false on worlds created before 19w36a.

Steps to Reproduce:
1. Open a world created before you updated to 19w36a
2. In survival mode jump off a height of more than 4 blocks
3. You will not take fall damage