progress: ratelimit/progress tweaks

- multi.c: when ratelimiting a transfer stops (MSTATE_RATELIMITING ->
  MSTATE_PERFORMING), run the MSTATE_PERFORMING state right away

- urldata.h: factor out upload and download progress counters into a
  struct, use that for passing these to progress update functions

- progress.c/getinfo.c: change names of moved progress counters

- progress.c: use new structs and a helper struct to factor repeated
  calculation into static helpers

Closes #14335

lib/progress.h

@@ -58,10 +58,8 @@ void Curl_pgrsUpdate_nometer(struct Curl_easy *data);
 
 void Curl_pgrsResetTransferSizes(struct Curl_easy *data);
 struct curltime Curl_pgrsTime(struct Curl_easy *data, timerid timer);
-timediff_t Curl_pgrsLimitWaitTime(curl_off_t cursize,
-                                  curl_off_t startsize,
-                                  curl_off_t limit,
-                                  struct curltime start,
+timediff_t Curl_pgrsLimitWaitTime(struct pgrs_dir *d,
+                                  curl_off_t speed_limit,
                                   struct curltime now);
 /**
  * Update progress timer with the elapsed time from its start to `timestamp`.