Refactor pgp_encrypted_material_t to C++ classes. #3893

Job	Run time
cmake-offline-googletest	4m 22s
cmake-offline-googletest-src	4m 12s
package-source	32s
system-sexpp, sexpp shared libs on, rnp shared libs on	2m 57s
system-sexpp, sexpp shared libs on, rnp shared libs off	3m 20s
ubuntu-latest [CC gcc; botan; shared libs on; GnuPG stable]	4m 23s
system-sexpp, sexpp shared libs off, rnp shared libs on	3m 7s
ubuntu-latest [CC clang; botan; shared libs on; GnuPG stable]	4m 10s
system-sexpp, sexpp shared libs off, rnp shared libs off	3m 18s
ubuntu-latest [CC gcc; openssl; shared libs on; GnuPG stable]	4m 7s
ubuntu-latest [CC clang; openssl; shared libs on; GnuPG stable]	4m 2s
ubuntu-20.04 [CC gcc; openssl; shared libs on; GnuPG stable]	4m 5s
ubuntu-latest [CC gcc; botan; shared libs off; GnuPG stable]	3m 56s
package	1m 51s
debian-tests	10s
	48m 32s

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