refactor(configurations/browser/production): replace uglify with terser

[homer0]

What does this PR do?

It replaces uglifyjs-webpack-plugin with terser-webpack-plugin for bundle minification/uglification. The main reason is that uglifyjs doesn't support ES6+ code, and in the future, webpack will include terser as its default minification "engine".

Also, instead of adding terser to the plugins list, I'm adding it on the new optimization object, like the webpack documentation recommends.

This is breaking for plugin developers and in case you are using events to modify the configuration.

How should it be tested manually?

For an end user that is not modifying the configuration, the change is not breaking, so just install the branch and build for production, the minification should happen the same way as before.

And of course...

yarn test
# or
npm test

[coveralls]

Pull Request Test Coverage Report for Build 230

• 3 of 3 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

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Totals
Change from base Build 228:	0.0%
Covered Lines:	591
Relevant Lines:	591

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💛 - Coveralls