test: add some validation for JSON doc output #2599

Job	Run time
Build slim tarball	1m 35s
x86_64-linux: with shared libraries	30m 29s
aarch64-darwin: with shared libraries	33m 48s
aarch64-linux: with shared libraries	24m 19s
x86_64-darwin: with shared libraries	36m 29s
	2h 6m 40s

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