[CLEANUP] Extract method RuleSet::comparePositionable (#1272)

As well as being used with `usort()`, it may have other uses.

The deprecated `getLineNo()` and `getColNo()` are still used for now.
Replacing these will be done separately.

Relates to #974.

Author: JakeQZ

src/RuleSet/RuleSet.php

@@ -173,12 +173,7 @@ public function getRules(?string $searchPattern = null): array
                 $result = \array_merge($result, $rules);
             }
         }
-        \usort($result, static function (Rule $first, Rule $second): int {
-            if ($first->getLineNo() === $second->getLineNo()) {
-                return $first->getColNo() - $second->getColNo();
-            }
-            return $first->getLineNo() - $second->getLineNo();
-        });
+        \usort($result, [self::class, 'comparePositionable']);
 
         return $result;
     }
@@ -299,4 +294,15 @@ protected function renderRules(OutputFormat $outputFormat): string
 
         return $formatter->removeLastSemicolon($result);
     }
+
+    /**
+     * @return int negative if `$first` is before `$second`; zero if they have the same position; positive otherwise
+     */
+    private static function comparePositionable(Positionable $first, Positionable $second): int
+    {
+        if ($first->getLineNo() === $second->getLineNo()) {
+            return $first->getColNo() - $second->getColNo();
+        }
+        return $first->getLineNo() - $second->getLineNo();
+    }
 }