Add toRelativePath method to file system

Author: CodeDoctorDE

packages/lw_file_system/lib/src/api/file_system_base.dart

@@ -104,6 +104,17 @@ abstract class GeneralFileSystem {
     return variant;
   }
 
+  Future<String?> toRelativePath(String path) async {
+    final root = await getDirectory();
+    if (universalPathContext.isRelative(path)) {
+      return normalizePath(path);
+    }
+    if (universalPathContext.isWithin(root, path)) {
+      return universalPathContext.relative(path, from: root);
+    }
+    return null;
+  }
+
   Future<Uint8List?> loadAbsolute(String path) => Future.value(null);
 
   Future<void> saveAbsolute(String path, Uint8List bytes) => Future.value();

packages/lw_file_system/lib/src/api/file_system_html.dart

@@ -188,6 +188,9 @@ class WebDirectoryFileSystem extends DirectoryFileSystem with WebFileSystem {
     return doc != null;
   }
 
+  @override
+  Future<String?> toRelativePath(String path) => Future.value(null);
+
   @override
   Future<bool> updateFile(
     String path,

packages/lw_file_system/lib/src/api/file_system_io.dart

@@ -3,7 +3,6 @@ import 'dart:io';
 
 import 'package:flutter/foundation.dart';
 import 'package:lw_file_system/lw_file_system.dart';
-import 'package:path/path.dart' as p;
 import 'package:synchronized/synchronized.dart';
 
 Future<void> _updateFile((String, Uint8List) e) async {
@@ -134,7 +133,7 @@ class IODirectoryFileSystem extends DirectoryFileSystem {
           (await directory.list(followLinks: false).toList()).map((e) async {
             final current = universalPathContext.join(
               path,
-              p.relative(e.path, from: absolutePath),
+              universalPathContext.relative(e.path, from: absolutePath),
             );
             if (e is File) {
               return RawFileSystemFile(