tools/clang/json: escape strings properly #19062

Job	Run time
gvisor	4m 8s
dashboard	2m 37s
build	3m 8s
aux	4m 48s
old	7m 10s
race_dashboard	4m 4s
race	7m 15s
arch (presubmit_arch_darwin)	3m 54s
arch (presubmit_arch_windows)	3m 49s
arch (presubmit_arch_netbsd)	4m 6s
arch (presubmit_arch_freebsd)	6m 31s
arch (presubmit_arch_openbsd)	4m 12s
arch (presubmit_arch_executor)	3m 33s
arch (presubmit_arch_linux)	10m 51s
	1h 10m 6s

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