chore(lighthouse-viewer): replace deprecated uglify-es with terser

[wardpeet]

Summary
I'm replacing uglify-es with terser to minify our viewer.js. Terser has been the successor to uglify-es as it's not actively maintained anymore.

Related Issues/PRs
Fixes #9558

[connorjclark]

async/await will work now, yes?

don't change anything yet - I don't want conflicts w/ my viewer changes. one of use could follow up later and async/await the things here. just wanna ensure it works now :)

[wardpeet]

Yeah it will, it should have all es7-8 features.

[brendankenny]

LGTM

Thanks @wardpeet!

[brendankenny]

The one issue I see is the output isn't in strict mode since it no longer has a "use strict"; directive at the top. Is there any way to get terser to output that? I guess at worst we could add it to the preamble :/

[connorjclark]

The one issue I see is the output isn't in strict mode since it no longer has a "use strict"; directive at the top. Is there any way to get terser to output that? I guess at worst we could add it to the preamble :/

not seeing a way to get use strict in the toplevel for terser, but it still has use strict in various other parts of the minified code.

[wardpeet]

good catch @brendankenny, i've added the "use-strict"; pragma again.

[brendankenny]

good catch @brendankenny, i've added the "use-strict"; pragma again.

ah, nice fix :)

[patrickhulce]

LGTM