Add back CustomDebugStringConvertible conformance #1335

Job	Run time
Api Breakage Compared to main Branch	1m 44s
core (5.10.0-jammy, ref/heads/main)	12m 59s
fuzzing_regressions (debug)	4m 23s
core (5.9.2-jammy, SWIFT_BUILD_TEST_HOOK="-Xswiftc -warnings-as-errors", ref/heads/main)	12m 32s
fuzzing_regressions (release)	2m 55s
Api Breakage Compared to Last Release	1m 26s
core (5.8.1-jammy, SWIFT_BUILD_TEST_HOOK="-Xswiftc -warnings-as-errors", ref/heads/main)	12m 43s
sanitizer_testing (address, debug)	2m 26s
sanitizer_testing (address, release)	4m 51s
sanitizer_testing (thread, debug)	2m 30s
sanitizer_testing (thread, release)	4m 31s
	1h 3m 0s

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