Add additional EVP_SKEY helpers #477

Job	Run time
compiler (gcc-7, ubuntu-20.04)	4m 24s
compiler (gcc-8, ubuntu-20.04)	4m 35s
compiler (gcc-9, ubuntu-20.04)	4m 46s
compiler (gcc-10, ubuntu-20.04)	4m 24s
compiler (gcc-11, ubuntu-22.04)	4m 36s
compiler (gcc-12, ubuntu-22.04)	4m 59s
compiler (gcc-13, ubuntu-22.04, ubuntu-toolchain-r/test)	5m 22s
compiler (clang-6.0, ubuntu-20.04)	4m 51s
compiler (clang-7, ubuntu-20.04)	4m 46s
compiler (clang-8, ubuntu-20.04)	4m 50s
compiler (clang-9, ubuntu-20.04)	4m 57s
compiler (clang-10, ubuntu-20.04)	5m 0s
compiler (clang-11, ubuntu-20.04)	4m 58s
compiler (clang-12, ubuntu-20.04)	4m 54s
compiler (clang-13, ubuntu-22.04)	5m 2s
compiler (clang-14, ubuntu-22.04)	4m 59s
compiler (clang-15, ubuntu-22.04, jammy)	5m 12s
compiler (clang-16, ubuntu-22.04, jammy)	5m 24s
compiler (clang-17, ubuntu-22.04, jammy)	5m 20s
	1h 33m 19s

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