Refactor pgp_encrypted_material_t to C++ classes. #3878

Job	Run time
cmake-offline-googletest	4m 16s
cmake-offline-googletest-src	4m 27s
ubuntu-latest [CC gcc; botan; shared libs on; GnuPG stable]	4m 16s
ubuntu-latest [CC clang; botan; shared libs on; GnuPG stable]	4m 19s
ubuntu-latest [CC gcc; openssl; shared libs on; GnuPG stable]	4m 9s
ubuntu-latest [CC clang; openssl; shared libs on; GnuPG stable]	4m 5s
ubuntu-20.04 [CC gcc; openssl; shared libs on; GnuPG stable]	4m 5s
package-source	27s
system-sexpp, sexpp shared libs on, rnp shared libs on	3m 5s
ubuntu-latest [CC gcc; botan; shared libs off; GnuPG stable]	4m 9s
system-sexpp, sexpp shared libs on, rnp shared libs off	2m 53s
system-sexpp, sexpp shared libs off, rnp shared libs on	3m 17s
system-sexpp, sexpp shared libs off, rnp shared libs off	4m 31s
package	49s
debian-tests	9s
	48m 57s

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