Stop using Babel; compile JS to ES2020 #2724

Job	Run time
R-CMD-check / setup	1m 8s
routine / routine	4m 55s
website / pkgdown	3m 15s
R-CMD-check / macOS-latest (4.4.2)	3m 35s
R-CMD-check / windows-latest (4.4.2)	3m 44s
R-CMD-check / ubuntu-latest (devel)	5m 23s
R-CMD-check / ubuntu-latest (4.4.2)	8m 34s
R-CMD-check / ubuntu-latest (4.3.3)	5m 11s
R-CMD-check / ubuntu-latest (4.2.3)	6m 42s
R-CMD-check / ubuntu-latest (4.1.3)	5m 31s
R-CMD-check / ubuntu-latest (4.0.5)	6m 40s
	54m 38s

Provide feedback