chore(core): enable eslint/strict-boolean-expressions & strictNullChecks #2016

Job	Run time
setup-and-test (ubuntu-latest, 18.x)	2m 29s
setup-and-test (ubuntu-latest, 20.x)	2m 48s
Check coding style	13s
eslint	2m 0s
Check version consistency of packages	7s
	7m 37s

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