Use pg_ascii_tolower()/pg_ascii_toupper() where appropriate.

Avoids unnecessary dependence on setlocale(). No behavior change.

This commit reverts e1458f2f1b, which reverted some changes
unintentionally committed before the branch for 19.

Reviewed-by: Peter Eisentraut <peter@eisentraut.org>
Discussion: https://postgr.es/m/a8666c391dfcabe79868d95f7160eac533ace718.camel@j-davis.com
Discussion: https://postgr.es/m/7efaaa645aa5df3771bb47b9c35df27e08f3520e.camel@j-davis.com

contrib/isn/isn.c

@@ -726,7 +726,7 @@ string2ean(const char *str, struct Node *escontext, ean13 *result,
 			if (type != INVALID)
 				goto eaninvalid;
 			type = ISSN;
-			*aux1++ = toupper((unsigned char) *aux2);
+			*aux1++ = pg_ascii_toupper((unsigned char) *aux2);
 			length++;
 		}
 		else if (length == 9 && (digit || *aux2 == 'X' || *aux2 == 'x') && last)
@@ -736,7 +736,7 @@ string2ean(const char *str, struct Node *escontext, ean13 *result,
 				goto eaninvalid;
 			if (type == INVALID)
 				type = ISBN;	/* ISMN must start with 'M' */
-			*aux1++ = toupper((unsigned char) *aux2);
+			*aux1++ = pg_ascii_toupper((unsigned char) *aux2);
 			length++;
 		}
 		else if (length == 11 && digit && last)

contrib/spi/refint.c

@@ -321,7 +321,7 @@ check_foreign_key(PG_FUNCTION_ARGS)
 	if (nrefs < 1)
 		/* internal error */
 		elog(ERROR, "check_foreign_key: %d (< 1) number of references specified", nrefs);
-	action = tolower((unsigned char) *(args[1]));
+	action = pg_ascii_tolower((unsigned char) *(args[1]));
 	if (action != 'r' && action != 'c' && action != 's')
 		/* internal error */
 		elog(ERROR, "check_foreign_key: invalid action %s", args[1]);

src/backend/commands/copyfromparse.c

@@ -1538,7 +1538,7 @@ GetDecimalFromHex(char hex)
 	if (isdigit((unsigned char) hex))
 		return hex - '0';
 	else
-		return tolower((unsigned char) hex) - 'a' + 10;
+		return pg_ascii_tolower((unsigned char) hex) - 'a' + 10;
 }
 
 /*

src/backend/utils/adt/inet_net_pton.c

@@ -115,8 +115,7 @@ inet_cidr_pton_ipv4(const char *src, u_char *dst, size_t size)
 		src++;					/* skip x or X. */
 		while ((ch = *src++) != '\0' && isxdigit((unsigned char) ch))
 		{
-			if (isupper((unsigned char) ch))
-				ch = tolower((unsigned char) ch);
+			ch = pg_ascii_tolower((unsigned char) ch);
 			n = strchr(xdigits, ch) - xdigits;
 			assert(n >= 0 && n <= 15);
 			if (dirty == 0)