Add hook for customizing the debug representation of an object #1709

Job	Run time
ruby-versions / Generate Ruby versions	2s
test (2.7)	1m 47s
test (3.0)	1m 42s
test (3.1)	2m 4s
test (3.2)	1m 40s
test (3.3)	1m 43s
test (debug)	2m 14s
test (head)	1m 15s
	12m 27s

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