Data validation and conditional formats: anchor relative formulas on the top-left cell of all areas (#3152)

Excel writes the relative formulas of a multi-area rule for the top-left
cell of the whole sqref (lowest row, lowest column), whatever order the
areas are listed in. GridCraft anchored them on the first area listed, so
a validation on `H62:H68 H26:H27 H93:H95` with `MOD($H26,$F26)=0` checked
row 26 - 36 at H26 and refused valid input.

Add `RangeRef::top_left` and use it in validation checks, list sources,
pasting a validation, conditional format lookups and the formulas the
xlsx writer generates for text, blank and error rules.

crates/engine/src/cmd/edit/paste_special.rs

@@ -248,7 +248,7 @@ pub(super) fn paste_special(s: &mut Session, p: &Json) -> Result<Json> {
                 crate::cmd::data::remove_validation_cells(&mut sh.validations, &[RangeRef::new(dest, dest)]);
                 if let Some(mut dv) = rule {
                     // Relative references move with the rule, as pasted formulas do.
-                    let first = dv.ranges.first().map_or(sc, |r| r.start);
+                    let first = RangeRef::top_left(&dv.ranges).unwrap_or(sc);
                     dv.f1 = crate::cmd::data::move_rule_formula(&dv.f1, first, dest);
                     dv.f2 = dv.f2.map(|f| crate::cmd::data::move_rule_formula(&f, first, dest));
                     dv.ranges = vec![RangeRef::new(dest, dest)];