chore(v2): switch from uglifyjs-webpack-plugin to terser-webpack-plugin

[endiliey]

Motivation

Currently, we use uglify via uglifyjs-webpack-plugin.

Some history:

• uglifyjs-webpack-plugin < v1.0 used the minifier uglify-js
• however uglify-js does not support ES6, which resulted in a fork
  called uglify-es that was developed in the uglify-js repository,
  but under the harmony branch
• uglifyjs-webpack-plugin v1.x switched to uglify-es for ES6 support
• however uglify-es stopped being maintained:
  uglify-es is stale mishoo/UglifyJS#3156 (comment)
• which led to a fork called terser that has incorporated all of
  the unmerged PRs and will be where all new development occurs:
  https://github.com/fabiosantoscode/terser
• terser-webpack-plugin was created, which is the terser equivalent
  of uglifyjs-webpack-plugin:
  https://github.com/webpack-contrib/terser-webpack-plugin
• uglifyjs-webpack-plugin v2.x will be switching back to uglify-js,
  so any project that needs to support ES6 now needs to switch to
  terser-webpack-plugin.

Some references
Create-react-app use Terser
Webpack v5 will use terser plugin by default.
webpack/webpack#7923
webpack-contrib/terser-webpack-plugin#15

Have you read the Contributing Guidelines on pull requests?

Yes

Test Plan

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