Stop using Babel; compile JS to ES2020 #2740

Job	Run time
website / pkgdown	2m 54s
routine / routine	4m 30s
R-CMD-check / setup	55s
R-CMD-check / macOS-latest (4.4.2)	4m 27s
R-CMD-check / windows-latest (4.4.2)	3m 49s
R-CMD-check / ubuntu-latest (devel)	6m 39s
R-CMD-check / ubuntu-latest (4.4.2)	6m 54s
R-CMD-check / ubuntu-latest (4.3.3)	7m 52s
R-CMD-check / ubuntu-latest (4.2.3)	3m 51s
R-CMD-check / ubuntu-latest (4.1.3)	6m 15s
R-CMD-check / ubuntu-latest (4.0.5)	6m 27s
	54m 33s

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