Rewrite rule formulas for the new top-left cell when cells are removed from a rule

Clearing validation from cells (or setting a new rule, or pasting a
validation over them) and Clear Rules on selected cells shrink a rule's
areas. When that removes the rule's top-left cell, the relative formulas
were left written for the old cell, so the cells left checked other
cells: clearing A1 off a custom `A1>10` on A1:A9 made A2 check A1.

Rewrite the relative references of validation formulas, and of
conditional format expressions and comparison values, for the new
top-left cell. Absolute references and literal lists stay as they are.

crates/engine/src/cmd/insert.rs

@@ -1730,7 +1730,13 @@ fn clear_cf(s: &mut Session, p: &Json) -> Result<Json> {
             sh.cond_formats.clear();
         } else {
             for cf in sh.cond_formats.iter_mut() {
+                let before = RangeRef::top_left(&cf.ranges);
                 cf.ranges.retain(|r| !ranges.iter().any(|x| x.intersects(r)));
+                // The relative formulas are written for the top-left cell: when it goes, they're
+                // rewritten for the new one, so the areas left keep reading the same cells.
+                if let (Some(from), Some(to)) = (before, RangeRef::top_left(&cf.ranges)) {
+                    rebase_cf_formulas(&mut cf.rule, from, to);
+                }
             }
             sh.cond_formats.retain(|c| !c.ranges.is_empty());
         }
@@ -1738,6 +1744,19 @@ fn clear_cf(s: &mut Session, p: &Json) -> Result<Json> {
     })
 }
 
+/// Moves the relative references of a rule's per-cell formulas written for `from` to `to`.
+fn rebase_cf_formulas(rule: &mut CfRule, from: CellRef, to: CellRef) {
+    let mv = |f: &str| crate::cmd::data::move_rule_formula(f, from, to);
+    match rule {
+        CfRule::CellIs { a, b, .. } => {
+            *a = mv(a);
+            *b = b.as_deref().map(mv);
+        }
+        CfRule::Expression { formula, .. } => *formula = mv(formula),
+        _ => {}
+    }
+}
+
 fn manage_cf(s: &mut Session, p: &Json) -> Result<Json> {
     let sheet = target_sheet(s, p)?;
     if p.get("delete").is_none() && p.get("moveUp").is_none() && p.get("moveDown").is_none() {