Refactor pgp_encrypted_material_t to C++ classes. #3880

Job	Run time
cmake-offline-googletest	5m 8s
cmake-offline-googletest-src	4m 5s
system-sexpp, sexpp shared libs on, rnp shared libs on	3m 8s
package-source	27s
system-sexpp, sexpp shared libs on, rnp shared libs off	3m 16s
ubuntu-latest [CC gcc; botan; shared libs on; GnuPG stable]	4m 22s
system-sexpp, sexpp shared libs off, rnp shared libs on	3m 4s
ubuntu-latest [CC clang; botan; shared libs on; GnuPG stable]	4m 18s
system-sexpp, sexpp shared libs off, rnp shared libs off	2m 56s
ubuntu-latest [CC gcc; openssl; shared libs on; GnuPG stable]	4m 12s
ubuntu-latest [CC clang; openssl; shared libs on; GnuPG stable]	4m 15s
ubuntu-20.04 [CC gcc; openssl; shared libs on; GnuPG stable]	3m 52s
ubuntu-latest [CC gcc; botan; shared libs off; GnuPG stable]	5m 2s
package	1m 0s
debian-tests	10s
	49m 15s

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