fuzz: add target for `Descriptor::parse_descriptor` #2136

Job	Run time
Bench - nightly toolchain (recent)	3m 28s
Docs - nightly toolchain (recent)	39s
Docs - stable toolchain (recent)	1m 2s
Embedded	1m 50s
Format - nightly toolchain	13s
Lint - nightly toolchain (recent)	32s
Integration tests - stable toolchain (26_0)	45s
Integration tests - stable toolchain (25_2)	53s
Test - 1.63.0 toolchain (minimal)	24m 50s
Integration tests - stable toolchain (25_1)	48s
Test - nightly toolchain (minimal)	13m 45s
Test - 1.63.0 toolchain (recent)	25m 13s
Test - stable toolchain (minimal)	16m 17s
Integration tests - stable toolchain (25_0)	49s
Test - nightly toolchain (recent)	14m 43s
Test - stable toolchain (recent)	16m 20s
Integration tests - stable toolchain (24_2)	49s
Integration tests - stable toolchain (24_1)	53s
Integration tests - stable toolchain (24_0_1)	58s
Integration tests - stable toolchain (23_2)	55s
Integration tests - stable toolchain (23_1)	52s
Integration tests - stable toolchain (23_0)	49s
Integration tests - stable toolchain (22_1)	51s
Integration tests - stable toolchain (22_0)	48s
Integration tests - stable toolchain (0_21_2)	46s
Integration tests - stable toolchain (0_20_2)	47s
Integration tests - stable toolchain (0_19_1)	45s
Integration tests - stable toolchain (0_18_1)	49s
Integration tests - stable toolchain (0_17_1)	45s
	2h 12m 54s

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