lib: further send/upload handling polish

lib: further send/upload handling polish

- Move all the "upload_done" handling to request.c

  - add possibility to abort sending of a request
  - add `Curl_req_done_sending()` for checks
  - transfer.c: readwrite_upload() now clean

- removing data->state.ulbuf and data->req.upload_fromhere

  - as well as data->req.upload_present
  - set data->req.upload_done on having read all from
    the client and completely flushed the send buffer

- tftp, remove setting of data->req.upload_fromhere

  - serves no purpose as `upload_present` is not set
    and the data itself is directly `sendto()` anyway

- smtp, make upload EOB conversion a client reader
- xfer_ulbuf addition

  - add xfer_ulbuf for borrowing, similar to xfer_buf
  - use in file upload
  - use in c-hyper body sending

- h1-proxy, remove init of data->state.uilbuf that is never used
- smb, add own send_buf instead of using data->state.ulbuf

Closes #13010