lib: client writer, part 2, accounting + logging

This PR has these changes:

Renaming of unencode_* to cwriter, e.g. client writers
- documentation of sendf.h functions
- move max decode stack checks back to content_encoding.c
- define writer phase which was used as order before
- introduce phases for monitoring inbetween decode phases
- offering default implementations for init/write/close

Add type paramter to client writer's do_write()
- always pass all writes through the writer stack
- writers who only care about BODY data will pass other writes unchanged

add RAW and PROTOCOL client writers
- RAW used for Curl_debug() logging of CURLINFO_DATA_IN
- PROTOCOL used for updates to data->req.bytecount, max_filesize checks and
  Curl_pgrsSetDownloadCounter()
- remove all updates of data->req.bytecount and calls to
  Curl_pgrsSetDownloadCounter() and Curl_debug() from other code
- adjust test457 expected output to no longer see the excess write

Closes #12184

lib/progress.c

@@ -319,12 +319,6 @@ timediff_t Curl_pgrsLimitWaitTime(curl_off_t cursize,
  */
 CURLcode Curl_pgrsSetDownloadCounter(struct Curl_easy *data, curl_off_t size)
 {
-  if(data->set.max_filesize && (size > data->set.max_filesize)) {
-    failf(data, "Exceeded the maximum allowed file size "
-          "(%" CURL_FORMAT_CURL_OFF_T ")",
-          data->set.max_filesize);
-    return CURLE_FILESIZE_EXCEEDED;
-  }
   data->progress.downloaded = size;
   return CURLE_OK;
 }