Build: update browser build

[mysticatea]

What is the purpose of this pull request? (put an "X" next to item)

[X] Other, please explain: update the webpack configuration of browser tests and the online demo.

What changes did you make? (Give an overview)

This PR update our webpack configuration to not use regjsparser package as a follow up of #12662.

After this change, @babel/preset-env prints below:

Using targets:
{
  "chrome": "76",
  "edge": "18",
  "firefox": "69",
  "ios": "12.2",
  "safari": "12.1",
  "samsung": "10.1"
}

Using modules transform: auto

Using plugins:
  transform-template-literals { "ios":"12.2", "safari":"12.1" }
  transform-function-name { "edge":"18" }
  transform-dotall-regex { "edge":"18", "firefox":"69" }
  proposal-async-generator-functions { "edge":"18" }
  proposal-object-rest-spread { "edge":"18" }
  proposal-unicode-property-regex { "edge":"18", "firefox":"69" }
  proposal-json-strings { "edge":"18" }
  transform-named-capturing-groups-regex { "edge":"18", "firefox":"69" }
  syntax-dynamic-import { "chrome":"76", "edge":"18", "firefox":"69", "ios":"12.2", "opera":"63", "safari":"12.1", "samsung":"10.1" }

Using polyfills: No polyfills were added, since the `useBuiltIns` option was not set.

Is there anything you'd like reviewers to focus on?

Are the versions OK?

[kaicataldo]

LGTM, thanks!

[kaicataldo]

Thanks for contributing!