Add support for musig() key expressions #1116

Job	Run time
Compilation for NanoS, X, S+, and Stax (nanos, $NANOS_SDK)	1m 47s
Compilation for NanoS, X, S+, and Stax (nanox, $NANOX_SDK)	1m 51s
Compilation for NanoS, X, S+, and Stax (nanosp, $NANOSP_SDK)	1m 45s
Compilation for NanoS, X, S+, and Stax (stax, $STAX_SDK)	1m 54s
Tests (nanos)	8m 16s
Tests on mainnet (nanos)	32s
Tests (nanox)	8m 57s
Tests on mainnet (nanox)	34s
Unit test	2m 14s
Tests (nanosp)	9m 18s
Tests on mainnet (nanosp)	34s
Tests (stax)	54m 7s
Tests on mainnet (stax)	32s
Tests with the Python library and legacy Bitcoin app	46s
Tests with the JS library	1m 34s
Tests for rust client library	1m 36s
	1h 36m 17s

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