Add Flutter Console for Windows (#14030)

Just download a Flutter ZIP bundle, unzip, and double-click on `flutter_console.bat` to get started. No PATH modifications required.

flutter_console.bat

+@echo off
+REM Copyright 2017 The Chromium Authors. All rights reserved.
+REM Use of this source code is governed by a BSD-style license that can be
+REM found in the LICENSE file.
+
+TITLE Flutter Console
+COLOR 3f
+
+echo.
+echo          ######## ##       ##     ## ######## ######## ######## ########
+echo          ##       ##       ##     ##    ##       ##    ##       ##     ##
+echo          ##       ##       ##     ##    ##       ##    ##       ##     ##
+echo          ######   ##       ##     ##    ##       ##    ######   ########
+echo          ##       ##       ##     ##    ##       ##    ##       ##   ##
+echo          ##       ##       ##     ##    ##       ##    ##       ##    ##
+echo          ##       ########  #######     ##       ##    ######## ##     ##
+echo.
+echo.
+
+echo  WELCOME to the Flutter Console.
+echo  ================================================================================
+echo.
+echo  Use the console below this message to interact with the "flutter" command.
+echo  Run "flutter doctor" to check if your system is ready to run Flutter apps.
+echo  Run "flutter create <app_name>" to create a new Flutter project.
+echo.
+echo  Run "flutter help" to see all available commands.
+echo.
+echo  Want to use an IDE to interact with Flutter? https://flutter.io/ide-setup/
+echo.
+echo  Want to run the "flutter" command from any Command Prompt or PowerShell window?
+echo  Add Flutter to your PATH: https://flutter.io/setup-windows/#update-your-path
+echo.
+echo  ================================================================================
+
+REM "%~dp0" is the directory of this file including trailing backslash
+SET PATH=%~dp0bin;%PATH%
+
+CALL cmd /K "@echo off & cd %USERPROFILE% & echo on"