Improve tests speeds by reusing tabs

[corinagum]

Notes:

• Most of the time, the browser spent ~5 seconds to interpret webchat.js, the goal of reuse tab is to reduce 5 seconds to 1 second or less
• Our webchat.js for test is huge because we have instrumentation code for code coverage
• Reuse tab = reuse a single HTML page
• In our HTML tests, webchat.js is loaded via <script> tag at the top of the page
• It is not trivial to shutdown Web Chat because DirectLineJS cannot shut down cleanly (lingering connections)
• If a single test failed, we will need to restart the tab page and retry the test
  • Retry test also means, we will need to reset counter used by Jest snapshot

In the screenshot below, the quickest HTML test took 5.7 seconds to complete. Most tests took 10-11 seconds to complete. If run serially, it will take 1:28 hours to complete.