Refactor pgp_encrypted_material_t to C++ classes. #3892

Job	Run time
cmake-offline-googletest	4m 17s
cmake-offline-googletest-src	4m 22s
package-source	30s
system-sexpp, sexpp shared libs on, rnp shared libs on	2m 56s
system-sexpp, sexpp shared libs on, rnp shared libs off	2m 49s
ubuntu-latest [CC gcc; botan; shared libs on; GnuPG stable]	4m 21s
system-sexpp, sexpp shared libs off, rnp shared libs on	2m 49s
ubuntu-latest [CC clang; botan; shared libs on; GnuPG stable]	4m 11s
system-sexpp, sexpp shared libs off, rnp shared libs off	2m 58s
ubuntu-latest [CC gcc; openssl; shared libs on; GnuPG stable]	4m 18s
ubuntu-latest [CC clang; openssl; shared libs on; GnuPG stable]	3m 59s
ubuntu-20.04 [CC gcc; openssl; shared libs on; GnuPG stable]	4m 9s
ubuntu-latest [CC gcc; botan; shared libs off; GnuPG stable]	4m 12s
package	50s
debian-tests	9s
	46m 50s

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