Stop using Babel; compile JS to ES2020 (#4066) #2741

Job	Run time
R-CMD-check / setup	45s
routine / routine	4m 21s
website / pkgdown	3m 8s
R-CMD-check / macOS-latest (4.4.2)	3m 40s
R-CMD-check / windows-latest (4.4.2)	3m 51s
R-CMD-check / ubuntu-latest (devel)	5m 14s
R-CMD-check / ubuntu-latest (4.4.2)	5m 58s
R-CMD-check / ubuntu-latest (4.3.3)	6m 8s
R-CMD-check / ubuntu-latest (4.2.3)	5m 7s
R-CMD-check / ubuntu-latest (4.1.3)	6m 44s
R-CMD-check / ubuntu-latest (4.0.5)	5m 36s
	50m 32s

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