util: Allow non-separator coalescing parsing in extract_first_word

If EXTRACT_DONT_COALESCE_SEPARATORS is passed, then leading separators,
trailing separators and spans of multiple separators aren't skipped, and
empty arguments from before, after or between separators may be extracted.

src/basic/util.h

@@ -859,6 +859,7 @@ typedef enum ExtractFlags {
         EXTRACT_CUNESCAPE       = 2,
         EXTRACT_CUNESCAPE_RELAX = 4,
         EXTRACT_QUOTES          = 8,
+        EXTRACT_DONT_COALESCE_SEPARATORS = 16,
 } ExtractFlags;
 
 int extract_first_word(const char **p, char **ret, const char *separators, ExtractFlags flags);