Fix browser echo sample for IE11

[compulim]

Semi-fix #1618.

Proposed Changes

• Update all dependencies to latest version
  • Bump to botbuilder-core@4.5.0 and botframework-webchat@4.5.0
  • Removing unnecessary dependencies and plugins
• Configure Babel to target "minus 2 versions" and Internet Explorer 11
• Configure Webpack to transpile botbuilder-core because the package is targeting ESNext instead of ES5
• Use core-js and regenerator-runtime instead of deprecated @babel/polyfill

In order to fix this sample in IE11, we requires 3 more fixes from botbuilder-js project:

• Proxy object capability check is broken botbuilder-js#1073
• RegExp in removeMentionText is not supported in IE11 botbuilder-js#1075
• Use import from instead of require in testAdapter.ts botbuilder-js#1076

Hacking botbuilder-js to make the sample work until we bump

turnContext.js/removeMentionText

- var mentionNameMatch = mentions[i].text.match(/(?<=<at.*>)(.*?)(?=<\/at>)/i);
+ var mentionNameMatch = [];

internal.js

- if (Proxy && Proxy.revocable) {
+ if (typeof Proxy !== 'undefined' && Proxy.revocable) {

Testing

1. Test using Webpack development server
   1. npm start
   2. Browse to http://localhost:8080/ under IE11 and modern browsers
2. Test using Webpack production build
   1. npm run build
   2. npx serve dist
   3. Browse to http://localhost:5000/ under IE11 and modern browsers

[stevengum]

Looks good, just one piece of feedback regarding the dependency

[stevengum]

Can you use ~ instead of ^? We test the versions by minor, so 4.2 might not necessarily work with 4.5.