fix: a hole at sketch points drills into the part its sketch touches (#910)

Hole centres from a sketch now drill into the material on whichever side of the sketch plane it lies: material the spot starts in wins, then the nearest body ahead, else against the sketch normal as before. A sketch on a part's underside or below it now drills up into the part. Covers counterbores, through-all, edge and corner centres, patterns and reopening.

crates/doc/src/document.rs

@@ -485,7 +485,7 @@ pub enum FeatureKind {
         depth: Option<String>,
         #[serde(default)]
         hole: HoleKind,
-        /// Drill at these sketch points instead (one hole each, perpendicular to the sketch);
+        /// Drill at these sketch points instead (one hole each, perpendicular to the sketch, into the material: against the sketch normal, or along it when only that side has material);
         /// the holes follow the points when the sketch changes.
         #[serde(default, skip_serializing_if = "Option::is_none")]
         points: Option<SketchPoints>,