Reorganize and clarify API doc generator (#132353)

## Description

This cleans up a lot of issues with the API doc generation.

Here are the main changes:
 - Rename `dartdoc.dart` to `create_api_docs.dart`
 - Move the bulk of the operations out of `dev/bots/docs.sh` into `create_api_docs.dart`.
 - Delete `dashing_postprocess.dart` and `java_and_objc.dart` and incorporate those operations into `create_api_docs.dart`.
 - Refactor the doc generation into more understandable classes
 - Bump the snippets tool version to 0.4.0 (the latest one)
 - Centralize the information gathering about the Flutter repo into the new `FlutterInformation` class.
 - Clean up the directory handling, and convert to using the `file` package for all file and directory paths.
 - Add an `--output` option to docs.sh that specifies the location of the output ZIP file containing the docs.
   - Defaults to placing the output in `dev/docs/api_docs.zip` (i.e. where the previous code generates the file).
 - Moved all document generation into a temporary folder that is removed once the documents are generated, to avoid VSCode and other IDEs trying to index the thousands of HTML and JS files in the docs output.
 - Updated pubspec dependencies.

## Tests
 - Added tests for doc generation.

dev/tools/java_and_objc_doc.dart

@@ -1,97 +0,0 @@
-// Copyright 2014 The Flutter Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-import 'dart:io';
-import 'dart:math';
-
-import 'package:archive/archive.dart';
-import 'package:http/http.dart' as http;
-import 'package:path/path.dart' as path;
-
-const String kDocRoot = 'dev/docs/doc';
-
-/// This script downloads an archive of Javadoc and objc doc for the engine from
-/// the artifact store and extracts them to the location used for Dartdoc.
-Future<void> main(List<String> args) async {
-  final String engineVersion = File('bin/internal/engine.version').readAsStringSync().trim();
-  String engineRealm = File('bin/internal/engine.realm').readAsStringSync().trim();
-  if (engineRealm.isNotEmpty) {
-    engineRealm = '$engineRealm/';
-  }
-
-  final String javadocUrl = 'https://storage.googleapis.com/${engineRealm}flutter_infra_release/flutter/$engineVersion/android-javadoc.zip';
-  generateDocs(javadocUrl, 'javadoc', 'io/flutter/view/FlutterView.html');
-
-  final String objcdocUrl = 'https://storage.googleapis.com/${engineRealm}flutter_infra_release/flutter/$engineVersion/ios-objcdoc.zip';
-  generateDocs(objcdocUrl, 'objcdoc', 'Classes/FlutterViewController.html');
-}
-
-/// Fetches the zip archive at the specified url.
-///
-/// Returns null if the archive fails to download after [maxTries] attempts.
-Future<Archive?> fetchArchive(String url, int maxTries) async {
-  List<int>? responseBytes;
-  for (int i = 0; i < maxTries; i++) {
-    final http.Response response = await http.get(Uri.parse(url));
-    if (response.statusCode == 200) {
-      responseBytes = response.bodyBytes;
-      break;
-    }
-    stderr.writeln('Failed attempt ${i+1} to fetch $url.');
-
-    // On failure print a short snipped from the body in case it's helpful.
-    final int bodyLength = min(1024, response.body.length);
-    stderr.writeln('Response status code ${response.statusCode}. Body: ${response.body.substring(0, bodyLength)}');
-    sleep(const Duration(seconds: 1));
-  }
-  return responseBytes == null ? null : ZipDecoder().decodeBytes(responseBytes);
-}
-
-Future<void> generateDocs(String url, String docName, String checkFile) async {
-  const int maxTries = 5;
-  final Archive? archive = await fetchArchive(url, maxTries);
-  if (archive == null) {
-    stderr.writeln('Failed to fetch zip archive from: $url after $maxTries attempts. Giving up.');
-    exit(1);
-  }
-
-  final Directory output = Directory('$kDocRoot/$docName');
-  print('Extracting $docName to ${output.path}');
-  output.createSync(recursive: true);
-
-  for (final ArchiveFile af in archive) {
-    if (!af.name.endsWith('/')) {
-      final File file = File('${output.path}/${af.name}');
-      file.createSync(recursive: true);
-      file.writeAsBytesSync(af.content as List<int>);
-    }
-  }
-
-  /// If object then copy files to old location if the archive is using the new location.
-  final bool exists = Directory('$kDocRoot/$docName/objectc_docs').existsSync();
-  if (exists) {
-    copyFolder(Directory('$kDocRoot/$docName/objectc_docs'), Directory('$kDocRoot/$docName/'));
-  }
-
-  final File testFile = File('${output.path}/$checkFile');
-  if (!testFile.existsSync()) {
-    print('Expected file ${testFile.path} not found');
-    exit(1);
-  }
-  print('$docName ready to go!');
-}
-
-/// Copies the files in a directory recursively to a new location.
-void copyFolder(Directory source, Directory destination) {
-  source.listSync()
-  .forEach((FileSystemEntity entity) {
-    if (entity is Directory) {
-      final Directory newDirectory = Directory(path.join(destination.absolute.path, path.basename(entity.path)));
-      newDirectory.createSync();
-      copyFolder(entity.absolute, newDirectory);
-    } else if (entity is File) {
-      entity.copySync(path.join(destination.path, path.basename(entity.path)));
-    }
-  });
-}