descriptor: introduce several Taproot accessors #2038

Job	Run time
Docs - nightly toolchain (recent)	33s
Bench - nightly toolchain (recent)	1m 3s
Docs - stable toolchain (recent)	23s
Embedded	1m 11s
Format - nightly toolchain	14s
Lint - nightly toolchain (recent)	48s
Integration tests - stable toolchain (26_0)	1m 5s
Integration tests - stable toolchain (25_2)	1m 2s
Test - 1.63.0 toolchain (minimal)	25m 1s
Test - nightly toolchain (minimal)	14m 28s
Integration tests - stable toolchain (25_1)	53s
Test - stable toolchain (minimal)	16m 58s
Test - 1.63.0 toolchain (recent)	24m 59s
Test - nightly toolchain (recent)	14m 34s
Integration tests - stable toolchain (25_0)	1m 13s
Test - stable toolchain (recent)	17m 14s
Integration tests - stable toolchain (24_2)	51s
Integration tests - stable toolchain (24_1)	1m 42s
Integration tests - stable toolchain (24_0_1)	47s
Integration tests - stable toolchain (23_2)	58s
Integration tests - stable toolchain (23_1)	2m 5s
Integration tests - stable toolchain (23_0)	1m 2s
Integration tests - stable toolchain (22_1)	1m 50s
Integration tests - stable toolchain (22_0)	51s
Integration tests - stable toolchain (0_21_2)	52s
Integration tests - stable toolchain (0_20_2)	1m 45s
Integration tests - stable toolchain (0_19_1)	1m 49s
Integration tests - stable toolchain (0_18_1)	1m 2s
Integration tests - stable toolchain (0_17_1)	54s
	2h 18m 7s

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