urlapi: leaner with fewer allocs

Slightly faster with more robust code. Uses fewer and smaller mallocs.

- remove two fields from the URL handle struct
- reduce copies and allocs
- use dynbuf buffers more instead of custom malloc + copies
- uses dynbuf to build the host name in reduces serial alloc+free within
  the same function.
- move dedotdotify into urlapi.c and make it static, not strdup the input
  and optimize it by checking for . and / before using strncmp
- remove a few strlen() calls
- add Curl_dyn_setlen() that can "trim" an existing dynbuf

Closes #9408

lib/urlapi-int.h

@@ -25,10 +25,11 @@
  ***************************************************************************/
 #include "curl_setup.h"
 
-bool Curl_is_absolute_url(const char *url, char *scheme, size_t buflen);
+size_t Curl_is_absolute_url(const char *url, char *buf, size_t buflen);
 
 #ifdef DEBUGBUILD
-CURLUcode Curl_parse_port(struct Curl_URL *u, char *hostname, bool);
+CURLUcode Curl_parse_port(struct Curl_URL *u, struct dynbuf *host,
+                          bool has_scheme);
 #endif
 
 #endif /* HEADER_CURL_URLAPI_INT_H */