Extrude: a symmetric distance is the total thickness (#1260)

A symmetric solid extrude of 10 mm is now 10 mm thick, 5 mm each side of the sketch plane, and switching from One Side to Symmetric keeps the thickness entered. Under format 21 the extent records its convention; designs saved without it keep the per-side reading, so their geometry and parameters don't change. Fixes #1236.

Co-authored-by: Karl-VonRichter <Karl-VonRichter@users.noreply.github.com>

crates/doc/src/tests.rs

@@ -33,6 +33,7 @@ fn plate_doc() -> (Document, u64) {
             sketch: s,
             profiles: ProfileSel::All,
             extent: Extent {
+                convention: crate::ExtrudeConvention::LegacyPerSide,
                 distance: "20".into(),
                 direction: Direction::Positive,
                 distance2: None,
@@ -125,6 +126,7 @@ fn box_fillet_cut_timeline() {
             sketch: s2,
             profiles: ProfileSel::Points { points: vec![Vec2::new(20.0, 15.0)] },
             extent: Extent {
+                convention: crate::ExtrudeConvention::LegacyPerSide,
                 distance: "20".into(),
                 direction: Direction::Positive,
                 distance2: None,