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
- mov

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

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test457: verify --max-filesize with chunked encoding