Parameters: move user parameters up and down (#1323)

Fixes #1187. New parameters.move {name, before|after} reorders user parameters (the design's own params order, so it is saved with no format change, and undoable); the Parameters dialog's user rows get up/down buttons. Label in every catalog. I merged main in. Checked on main + this branch: cargo check --workspace, the engine parameters tests, the UI parameter_order test, and docs/features.md regenerates unchanged.

crates/doc/src/params.rs

@@ -352,6 +352,25 @@ impl Document {
         rows
     }
 
+    /// Move user parameter `name` to just before (or with `after`, just after) user parameter
+    /// `target`: the order the Parameters dialog lists them in. Nothing else changes.
+    pub fn move_user_param(&mut self, name: &str, target: &str, after: bool) -> Result<()> {
+        fn user(params: &[crate::Param], n: &str) -> Option<usize> {
+            params.iter().position(|p| p.name == n && !p.model)
+        }
+        let (Some(from), Some(_)) = (user(&self.params, name), user(&self.params, target)) else {
+            let missing = if user(&self.params, name).is_none() { name } else { target };
+            return Err(DocError::Unknown(format!("user parameter `{missing}`")));
+        };
+        if name == target {
+            return Err(DocError::Invalid("a parameter cannot move next to itself".into()));
+        }
+        let moved = self.params.remove(from);
+        let at = user(&self.params, target).map_or(self.params.len(), |i| if after { i + 1 } else { i });
+        self.params.insert(at, moved);
+        Ok(())
+    }
+
     pub fn set_favorite(&mut self, name: &str, on: bool) -> Result<()> {
         if !self.name_taken(name) {
             return Err(DocError::Unknown(format!("parameter `{name}`")));