Biome masks do not account for edge blending

**Versions**
WorldEdit version: 7.2.0-SNAPSHOT+5347-8e53aa0
Platform version: forge-1.16.3-34.0.0

**Describe the bug**

Biome masks are restricted to 4x4x4 increments as they are defined, even though in-game the edges are smoothed to have a more natural feel.

**To Reproduce**
1. select a region. convert this area to a different biome.
2. set a mask to that biome, then set a region larger than the original to stone. the affected area is the 4x4x4 increments rather than the exact blocks appeared.

I can understand this happening in the case of setting a biome to a different one without affecting the others, but it seems like there could be a way to use the unblended version for biome setting and blended for other operations. I have realized that the game does not yet register vertical biome data, so this could be left untouched for now.

**What happened**

**What I expected**