Add get_key_string method to RuntimeEvent #3941

Job	Run time
cargo-doc-artifact	27m 34s
check-licenses	34s
check-demo-rollup-table-of-contents	11s
check	2m 53s
test	2m 57s
coverage	4m 24s
nextest	4m 12s
validate-packages-to-publish-yml	33s
features	21m 39s
check-demo-rollup-bash-commands	6m 13s
deploy-github-pages	0s
check-aggregate	3s
	1h 11m 13s

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