Save ZJIT stats_string to JSON output for stats collection #1703

Job	Run time
benchmark-run-once	1m 35s
benchmark-ractor-only (head)	36s
benchmark-ractor (head)	6m 45s
benchmark-graph	49s
test (truffleruby)	1m 53s
benchmark-default (head)	13m 33s
benchmark-default (ruby)	13m 18s
test (ruby)	52s
test (head)	47s
benchmark-default (truffleruby, --excludes=knucleotide,lobsters,ruby-lsp,shipit)	13m 5s
all-tests	2s
	53m 15s

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