tree-wide: check more log message format in log_struct() and friends

This introduce LOG_ITEM() macro that checks arbitrary formats in
log_struct().
Then, drop _printf_ attribute from log_struct_internal(), as it does not
help so much, and compiler checked only the first format string.

Hopefully, this silences false-positive warnings by Coverity.

src/cryptsetup/cryptsetup.c

@@ -1038,11 +1038,11 @@ static int measure_volume_key(
                 return log_error_errno(r, "Could not extend PCR: %m");
 
         log_struct(LOG_INFO,
-                   "MESSAGE_ID=" SD_MESSAGE_TPM_PCR_EXTEND_STR,
+                   LOG_MESSAGE_ID(SD_MESSAGE_TPM_PCR_EXTEND_STR),
                    LOG_MESSAGE("Successfully extended PCR index %u with '%s' and volume key (banks %s).", arg_tpm2_measure_pcr, s, joined),
-                   "MEASURING=%s", s,
-                   "PCR=%u", arg_tpm2_measure_pcr,
-                   "BANKS=%s", joined);
+                   LOG_ITEM("MEASURING=%s", s),
+                   LOG_ITEM("PCR=%u", arg_tpm2_measure_pcr),
+                   LOG_ITEM("BANKS=%s", joined));
 
         return 0;
 #else