fuzz: add target for `Descriptor::parse_descriptor` #2138

Job	Run time
Docs - stable toolchain (recent)	33s
Docs - nightly toolchain (recent)	38s
Bench - nightly toolchain (recent)	3m 34s
Embedded	1m 43s
Format - nightly toolchain	15s
Integration tests - stable toolchain (26_0)	48s
Lint - nightly toolchain (recent)	39s
Integration tests - stable toolchain (25_2)	48s
Test - 1.63.0 toolchain (minimal)	25m 44s
Integration tests - stable toolchain (25_1)	1m 41s
Test - nightly toolchain (minimal)	13m 52s
Test - 1.63.0 toolchain (recent)	26m 6s
Integration tests - stable toolchain (25_0)	1m 42s
Test - stable toolchain (minimal)	15m 44s
Test - nightly toolchain (recent)	13m 52s
Test - stable toolchain (recent)	16m 18s
Integration tests - stable toolchain (24_2)	51s
Integration tests - stable toolchain (24_1)	1m 44s
Integration tests - stable toolchain (24_0_1)	1m 54s
Integration tests - stable toolchain (23_2)	1m 41s
Integration tests - stable toolchain (23_1)	1m 49s
Integration tests - stable toolchain (23_0)	1m 17s
Integration tests - stable toolchain (22_1)	1m 12s
Integration tests - stable toolchain (22_0)	1m 14s
Integration tests - stable toolchain (0_21_2)	46s
Integration tests - stable toolchain (0_20_2)	45s
Integration tests - stable toolchain (0_19_1)	1m 11s
Integration tests - stable toolchain (0_18_1)	1m 21s
Integration tests - stable toolchain (0_17_1)	1m 8s
	2h 20m 50s

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