tree-wide: Load libcrypto and libssl via dlopen()

Until now OpenSSL was linked into every binary and library that needed
cryptography, pulling libcrypto (and, for resolved, libssl) into the
address space of services that never touch them at runtime. This commit
moves all OpenSSL usage behind the same dlopen helper pattern that we
already use for other optional libraries (libpam, libseccomp, libxz, …)
so libcrypto/libssl are only loaded on demand.

The bulk of the work lives in src/shared/crypto-util.{c,h} (libcrypto)
and src/shared/ssl-util.{c,h} (libssl), which replace the previous
src/shared/openssl-util.{c,h}:

 - crypto-util.{c,h} declares every libcrypto function we call via
   DLSYM_PROTOTYPE() and resolves them inside dlopen_libcrypto().

 - ssl-util.{c,h} holds the libssl-specific DLSYM_PROTOTYPEs,
   dlopen_libssl(), and the SSL_freep cleanup helper, so translation
   units that only need libcrypto do not pull in libssl declarations.

 - Callers refer to the symbols through sym_* aliases rather than the
   original names.

 - Convenience macros that used to be provided by the OpenSSL headers
   (OPENSSL_free, BN_num_bytes, the sk_TYPE_* helpers, …) are
   reimplemented as sym_* wrappers so no code path needs to fall back
   to the linker-resolved symbols.

 - All _cleanup_ helpers are redefined in terms of the sym_* variants
   (EVP_PKEY_freep, X509_freep, BIO_freep, …) so cleanup attributes
   keep working without pulling in libcrypto symbols at link time.

 - The public crypto-util.c entry points (openssl_pubkey_from_pem,
   openssl_digest_many, openssl_hmac_many, openssl_cipher_many,
   kdf_ss_derive, kdf_kb_hmac_derive, rsa_* / ecc_* helpers,
   pubkey_fingerprint, digest_and_sign, pkcs7_new, x509_fingerprint,
   openssl_extract_public_key, pkey_generate_volume_keys, the load_*
   helpers, …) now call dlopen_libcrypto() at entry before touching any
   sym_* pointer.

The call sites across the tree have been converted to call
dlopen_libcrypto()/dlopen_libssl() at the appropriate entry point
before their first sym_* use, and to use sym_* variants throughout:

 - bootctl, sbsign, measure, pcrlock, pcrextend, tpm2-setup, repart,
   cryptsetup, cryptenroll, homectl, homed, homework, keyutil,
   sysupdate, creds, import, dissect-image, pe-binary, pkcs11-util,
   pkcs7-util, tpm2-util, creds-util. resolved additionally dlopens
   libssl for DoT.

The meson build files are updated to depend on libopenssl_cflags (a
new partial dependency that exposes include paths and compile flags
only, not the linker flags) instead of libopenssl for every target that
previously linked against OpenSSL. Nothing links against libcrypto or
libssl directly anymore.

A new src/sbsign/authenticode.c hosts the Authenticode ASN.1 type
definitions that used to live inline in sbsign.c. The OpenSSL
ASN1_SEQUENCE / ASN1_CHOICE / IMPLEMENT_ASN1_FUNCTIONS macros expand to
code that references libcrypto symbols directly, so to keep this
translation unit unlinked from libcrypto we redirect ASN1_item_* to
the sym_* variants via #define and wrap the ASN1_*_it() getters (which
appear as constant function pointers in static initializers) in small
trampoline functions that forward to the sym_* pointers at runtime.

test-dlopen-so gains assertions for dlopen_libcrypto and dlopen_libssl
so the dlopen contract is exercised in CI, and the openssl-specific
test was renamed from test-openssl.c to test-crypto-util.c to match
the new header naming.

src/basic/basic-forward.h

@@ -69,6 +69,15 @@ struct fdisk_context;
 struct fdisk_table;
 struct crypt_device;
 
+typedef struct buf_mem_st BUF_MEM;
+typedef struct evp_pkey_st EVP_PKEY;
+typedef struct evp_md_st EVP_MD;
+typedef struct evp_md_ctx_st EVP_MD_CTX;
+typedef struct ssl_st SSL;
+typedef struct ssl_ctx_st SSL_CTX;
+typedef struct ssl_session_st SSL_SESSION;
+typedef struct x509_st X509;
+
 /* basic/ forward declarations */
 
 typedef void (*hash_func_t)(const void *p, struct siphash *state);
@@ -111,6 +120,7 @@ typedef struct Set Set;
 
 typedef struct dual_timestamp dual_timestamp;
 typedef struct triple_timestamp triple_timestamp;
+typedef struct Compressor Compressor;
 typedef struct ConfFile ConfFile;
 typedef struct LockFile LockFile;
 typedef struct PidRef PidRef;