tool: add curl command line option --trace-ids

- added and documented --trace-ids to prepend (after the timestamp)
  the transfer and connection identifiers to each verbose log line
- format is [n-m] with `n` being the transfer id and `m` being the
  connection id. In case there is not valid connection id, print 'x'.
- Log calls with a handle that has no transfer id yet, are written
  without any ids.

Closes #11185

docs/TheArtOfHttpScripting.md

@@ -64,6 +64,17 @@
 
     curl --trace-ascii d.txt --trace-time http://example.com/
 
+## See which Transfer
+
+ When doing parallel transfers, it is relevant to see which transfer is
+ doing what. When response headers are received (and logged) you need to
+ know which transfer these are for.
+ [`--trace-ids`](https://curl.se/docs/manpage.html#--trace-ids) option
+ is what you need. It will prepend the transfer and connection identifier
+ to each trace output line:
+
+    curl --trace-ascii d.txt --trace-ids http://example.com/
+
 ## See the Response
 
  By default curl sends the response to stdout. You need to redirect it

docs/cmdline-opts/Makefile.inc

@@ -265,6 +265,7 @@ DPAGES = \
   tlsv1.d \
   tr-encoding.d \
   trace-ascii.d \
+  trace-ids.d \
   trace-time.d \
   trace.d \
   unix-socket.d \

docs/cmdline-opts/trace-ids.d

@@ -0,0 +1,12 @@
+c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
+SPDX-License-Identifier: curl
+Long: trace-ids
+Help: Add transfer and connection identifiers to trace/verbose output
+Added: 8.2.0
+Category: verbose
+Example: --trace-ids --trace-ascii output $URL
+See-also: trace verbose
+Multi: boolean
+Scope: global
+---
+Prepends the transfer and connection identifiers to each trace or verbose line that curl displays.

docs/cmdline-opts/trace.d

@@ -7,7 +7,7 @@ Mutexed: verbose trace-ascii
 Category: verbose
 Example: --trace log.txt $URL
 Added: 7.9.7
-See-also: trace-ascii trace-time
+See-also: trace-ascii trace-ids trace-time
 Multi: single
 Scope: global
 ---

docs/options-in-versions

@@ -252,6 +252,7 @@
 --tr-encoding                        7.21.6
 --trace                              7.9.7
 --trace-ascii                        7.9.7
+--trace-ids                          8.2.0
 --trace-time                         7.14.0
 --unix-socket                        7.40.0
 --upload-file (-T)                   4.0