Add a descriptor object for ExtensionRange. #1160

Job	Run time
api-breakage	1m 35s
core (5.9.2-jammy, ref/heads/main)	12m 41s
sanitizer_testing (address, debug)	2m 23s
fuzzing_regressions (debug)	4m 26s
core (5.8.1-jammy, ref/heads/main)	12m 29s
sanitizer_testing (address, release)	5m 17s
fuzzing_regressions (release)	3m 3s
sanitizer_testing (thread, debug)	2m 30s
core (5.7.3-jammy, ref/heads/main)	10m 6s
sanitizer_testing (thread, release)	4m 35s
	59m 5s

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