Bump deps and min SDKs, move web apps to new bootstrapping logic (#2292)

Also removed the web measurement experiment from the material 3 demo

web/_packages/web_startup_analyzer/example/lib/main.dart

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// ignore_for_file: avoid_print
+
 import 'dart:convert';
 
 import 'package:flutter/material.dart';