Cave vines have different ID naming systems from other plants

Whereas twisting vines, weeping vines and kelp have the naming system <plant> and <plant>_plant, cave vines use cave_vines_head and cave_vines_body, making them inconsistent with everything else.

Steps to reproduce:

1. Type

   /setblock ~ ~ ~ cave_vin

2. See the suggestions cave_vines_body and cave_vines_head

3. Type

   /setblock ~ ~ ~ kel

4. See the suggestions kelp and kelp_plant

5. Type

   /setblock ~ ~ ~ weeping_vi

6. See the suggestions weeping_vines and weeping_vines_plant

7. Type

   /setblock ~ ~ ~ twisted_vi

8. See the suggestions twisted_vines and twisted_vines_plant