strbuf: bring back is_rfc3986_unreserved

is_rfc3986_unreserved() was moved to credential-store.c and was made
static by f89854362c (credential-store: move related functions to
credential-store file, 2023-06-06) under a correct assumption, at the
time, that it was the only place using it.

However now we need it to apply URL-encoding to submodule names when
constructing gitdir paths, to avoid conflicts, so bring it back.

Signed-off-by: Adrian Ratiu <adrian.ratiu@collabora.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/credential-store.c

@@ -76,12 +76,6 @@ static void rewrite_credential_file(const char *fn, struct credential *c,
 		die_errno("unable to write credential store");
 }
 
-static int is_rfc3986_unreserved(char ch)
-{
-	return isalnum(ch) ||
-		ch == '-' || ch == '_' || ch == '.' || ch == '~';
-}
-
 static int is_rfc3986_reserved_or_unreserved(char ch)
 {
 	if (is_rfc3986_unreserved(ch))

strbuf.c

@@ -817,6 +817,12 @@ void strbuf_addstr_xml_quoted(struct strbuf *buf, const char *s)
 	}
 }
 
+int is_rfc3986_unreserved(char ch)
+{
+	return isalnum(ch) ||
+		ch == '-' || ch == '_' || ch == '.' || ch == '~';
+}
+
 static void strbuf_add_urlencode(struct strbuf *sb, const char *s, size_t len,
 				 char_predicate allow_unencoded_fn)
 {

strbuf.h

@@ -640,6 +640,8 @@ static inline void strbuf_complete_line(struct strbuf *sb)
 
 typedef int (*char_predicate)(char ch);
 
+int is_rfc3986_unreserved(char ch);
+
 void strbuf_addstr_urlencode(struct strbuf *sb, const char *name,
 			     char_predicate allow_unencoded_fn);