Apply domain warp seed offset exactly once

[Auburn]

Problem

The domain warp seed offset was applied inconsistently. DomainWarp::GenT added mSeedOffset, then the Gradient and Simplex Warp() overloads added it again. The SuperSimplex Warp() overloads never added it. DomainWarpFractal* calls Warp() directly, bypassing GenT.

Warp node	Used directly	Inside DomainWarpFractal
Gradient / Simplex	seed + 2× offset	seed + offset
SuperSimplex	seed + offset	seed (offset ignored)

Fix

Remove the add from GenT, and add it to the SuperSimplex Warp() overloads. The offset is now applied exactly once, inside Warp(), for every warp type and whichever way it's used.

Output change

Only affects warps with a non-zero Seed Offset:

• Gradient and Simplex warps used directly.
• SuperSimplex warps inside a fractal warp.

Testing

• A warp with offset k at seed s must equal the same warp with offset 0 at seed s + k. I checked this for Gradient, Simplex and SuperSimplex, both directly and inside DomainWarpFractalProgressive, in 2D, 3D and 4D, on SSE2, SSE4.1, AVX2 and AVX512.
  • Before: Gradient/Simplex failed when used directly, and SuperSimplex failed inside the fractal.
  • After: all pass.
• No output changes for the default offset of 0.