Fix more format truncation issues

Fix the warnings created by the compiler warning options
-Wformat-overflow=2 -Wformat-truncation=2, supported since GCC 7.  This
is a more aggressive variant of the fixes in
6275f5d28a, which GCC 7 warned about by
default.

The issues are all harmless, but some dubious coding patterns are
cleaned up.

One issue that is of external interest is that BGW_MAXLEN is increased
from 64 to 96.  Apparently, the old value would cause the bgw_name of
logical replication workers to be truncated in some circumstances.

But this doesn't actually add those warning options.  It appears that
the warnings depend a bit on compilation and optimization options, so it
would be annoying to have to keep up with that.  This is more of a
once-in-a-while cleanup.

Reviewed-by: Michael Paquier <michael@paquier.xyz>

src/interfaces/libpq/fe-secure-openssl.c

@@ -1436,7 +1436,7 @@ PQsslAttribute(PGconn *conn, const char *attribute_name)
 
 	if (strcmp(attribute_name, "key_bits") == 0)
 	{
-		static char sslbits_str[10];
+		static char sslbits_str[12];
 		int			sslbits;
 
 		SSL_get_cipher_bits(conn->ssl, &sslbits);