Add support for musig() key expressions #1258

Job	Run time
Compilation for NanoS, X, S+, and Stax (nanos, $NANOS_SDK)	1m 43s
Compilation for NanoS, X, S+, and Stax (nanox, $NANOX_SDK)	1m 57s
Compilation for NanoS, X, S+, and Stax (nanosp, $NANOSP_SDK)	1m 55s
Compilation for NanoS, X, S+, and Stax (stax, $STAX_SDK)	2m 0s
Tests on mainnet (nanos)	29s
Unit test	2m 18s
Tests on mainnet (nanox)	29s
Tests with the Python library and legacy Bitcoin app	41s
Tests with the JS library	1m 14s
Tests on mainnet (nanosp)	33s
Tests on mainnet (stax)	27s
Tests for rust client library	1m 41s
	15m 27s

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