[Experimental] Nether Features Generate At Ceiling Thats Exposed To Air

Summary: Nether Roots and Vines and Wart Blocks can Generate on the Roof or Ceiling below y 128 thats exposed to air.

Steps To Reproduce:
Step 1: Go to Nether in 1.17.30.23 with Caves n Cliffs Toggle Enabled.
Step 2: Locate Warped or Crimson Biome.
Step 3: Fly Around.
Step 4: Repeat.

Observed Result: Nether Features Generate on Ceiling.

Expected Result: Nether Features Shouldn't Generate on Ceiling.