[Web] Release picked file data for Web

[tddang-linagora]

Issue

There's a memory leak happening with web version

Reproducible code

See here

import 'package:file_picker/file_picker.dart';
import 'package:flutter/material.dart';

void main() => runApp(const MyApp());

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Material App',
      home: FirstScreen(),
    );
  }
}

class FirstScreen extends StatelessWidget {
  const FirstScreen({super.key});

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: TextButton(
          onPressed: () {
            Navigator.push(
              context,
              MaterialPageRoute(builder: (context) => const SecondScreen()),
            );
          },
          child: Text('Go to second screen'),
        ),
      ),
    );
  }
}

class SecondScreen extends StatefulWidget {
  const SecondScreen({super.key});

  @override
  State<SecondScreen> createState() => _SecondScreenState();
}

class _SecondScreenState extends State<SecondScreen> {
  String _name = '';

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            Text("Picked file's name: $_name"),
            TextButton(
              onPressed: () async {
                final picked = await FilePicker.platform.pickFiles(
                  type: FileType.image,
                  withData: true,
                );
                if (mounted && picked != null) {
                  setState(() {
                    _name = picked.files.firstOrNull?.name ?? '';
                  });
                }
              },
              child: Text('Pick image'),
            ),
            TextButton(
              onPressed: () {
                Navigator.pop(context);
              },
              child: Text('Go back'),
            ),
          ],
        ),
      ),
    );
  }
}

Steps to reproduce

1. Run flutter run -d chrome --profile
2. Open Chrome dev tools, Memory tab, trigger garbage collector then snapshot main heap
3. Navigate to second screen by clicking on Go to second screen button
4. Pick a heavy file. In the above code, I chose to pick image because I already have a heavy image (16.3mb)
5. Go back to the previous screen either by clicking on Go back or any conventional ways for web
6. Trigger garbage collector then snapshot main heap again. Compare two snapshots.

Expected behavior

The file's data will be deallocated from memory

Actual behavior

The file's data is still on memory

Resolved demo

Before

After

[amrgetment]

as my PR for WASM support got merged you need to update clear children, check the file changes here
https://github.com/miguelpruivo/flutter_file_picker/pull/1481/files

[tddang-linagora]

as my PR for WASM support got merged you need to update clear children, check the file changes here https://github.com/miguelpruivo/flutter_file_picker/pull/1481/files

Right. Thank you.