Add alternate array index style, with setting

src/Settings.php

@@ -16,6 +16,8 @@ class Settings
 
     public static bool $tailLine = true;
 
+    public static bool $highlightIndices = true;
+
     public static function load(string $filename): void
     {
         if (file_exists($filename) && is_readable($filename)) {
@@ -25,6 +27,7 @@ class Settings
             self::$indentationGuides = $data->indentationGuides ?? true;
             self::$collapseBefore = $data->collapseBefore ?? true;
             self::$tailLine = $data->tailLine ?? true;
+            self::$highlightIndices = $data->highlightIndices ?? true;
         }
     }
 
@@ -37,6 +40,7 @@ class Settings
             'collapseBefore' => self::$collapseBefore,
             'highlightRow' => self::$highlightRow,
             'tailLine' => self::$tailLine,
+            'highlightIndices' => self::$highlightIndices,
         ], JSON_UNESCAPED_SLASHES|JSON_PRETTY_PRINT)."\n";
         @file_put_contents($filename, $data);
     }