refactor(generator): delete the pre-operator-stack archetype functions

With the operator stack as the only density path, the per-archetype
density functions have no caller left in the game:

- Delete UVoxelGenerator::GetSlabDensity, GetMazeDensity,
  GetSurfaceDensity, SurfaceDensityFromColumn, GetVerticalShaftDensity
  and GetFloatingIslandDensity (~1000 lines) with their declarations.
- Drop GetDensityWithParams' OutWarpedPosition out-parameter; only
  the native GetDensityAt branch removed in the previous commit used it.
- OpStack Slab/Maze/VerticalShaft/FloatingIsland and SurfaceHeight
  tests: remove the stack-vs-legacy comparisons; keep decomposition,
  finiteness, liveness, window-invariance, cache-cost and box-verdict
  checks (Shaft cache timing now measures the stack source).
- PassageLandsInOpenSpace: the source-only footing probe evaluates
  the archetype stack built without a strate manager instead of the
  deleted functions.
- Comments that cited the deleted functions now cite the operators
  (FSlabVoidSource, FLatticeCorridorSource, FIslandBlobSource, ...).
  GSurfColCache is documented as ClassifyTile's column cache.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01URDGLsu7c4nunqNFPJEFPU

Source/VoxelForge/Private/VoxelCaveMorphology.cpp

@@ -5303,9 +5303,9 @@ namespace
     }
 
     // The slab source is an XY height band. Evaluate the same two pure height fields as
-    // GetSlabDensity, then choose their midpoint after intersecting the seal-free interior.
+    // FSlabVoidSource, then choose their midpoint after intersecting the seal-free interior.
     // La source slab est une bande de hauteurs XY : on recalcule les deux champs purs comme
-    // GetSlabDensity, puis on prend leur milieu après intersection avec l'intérieur sans seal.
+    // FSlabVoidSource, puis on prend leur milieu après intersection avec l'intérieur sans seal.
     bool VF_SuggestSlabLandingPoint(
         const FSlabGenerationParams& Params,
         int32 Seed,
@@ -5444,7 +5444,8 @@ namespace
 
     // Maze corridors are lattice edges. Only a horizontal edge is a useful landing source: a
     // vertical edge can prove air, but cannot prove a place to stand. The edge set and Z levels
-    // below use the same origin-directed tree + loop contract as GetMazeDensity, with no cache.
+    // below use the same origin-directed tree + loop contract as FLatticeCorridorSource, with no
+    // cache.
     bool VF_SuggestMazeLandingPoint(
         const FMazeGenerationParams& Params,
         int32 Seed,
@@ -5879,7 +5880,7 @@ namespace
     };
 
     // Evaluate only the island source, in the same internal-density convention as
-    // GetFloatingIslandDensity (positive = solid, negative = void). This is intentionally a
+    // FIslandBlobSource (positive = solid, negative = void). This is intentionally a
     // local pure evaluator: it lets the query bracket the actual blob top instead of treating a
     // nominal island centre as footing. Full-octave noise is used because this query has no LOD
     // state by design and GeneratePassages runs before a tile's LOD is selected.
@@ -5916,7 +5917,7 @@ namespace
         for (int32 IslandIndex = 0; IslandIndex < NumIslands; ++IslandIndex)
         {
             const FVFIslandSite& Island = Islands[IslandIndex];
-            // Production GetFloatingIslandDensity evaluates exactly this 3x3 cell neighbourhood
+            // Production FIslandBlobSource evaluates exactly this 3x3 cell neighbourhood
             // for the queried XY. The outer search may collect more candidates so a lateral snap
             // can be found, but those distant blobs must not influence the returned footing.
             if (FMath::Abs(Island.CellX - BaseCellX) > 1