Farmland can be trampled by players in adventure mode

Players in adventure mode can trample farmland by jumping or falling onto it. This is annoying for making adventure maps, as players in adventure mode aren't supposed to be able to interact with the world. 

This is also an issue on Java Edition, and has already been reported there.

Steps to Reproduce:

1. Place farmland next to water
2. Switch to Adventure mode
3. Jump on the farmland

Observed Results:
The farmland is trampled.

Expected Results:
The farmland should not be trampled.