Improve logging of bad parameter values in BIND messages.

 Improve logging of bad parameter values in BIND messages.
 
 Since commit ba79cb5dc, values of bind parameters have been logged
 during errors in extended query mode.  However, we only did that after
 we'd collected and converted all the parameter values, thus failing to
 offer any useful localization of invalid-parameter problems.  Add a
 separate callback that's used during parameter collection, and have it
 print the parameter number, along with the input string if text input
 format is used.
 
 Justin Pryzby and Tom Lane
 
 Discussion: https://postgr.es/m/20210104170939.GH9712@telsasoft.com
 Discussion: https://postgr.es/m/CANfkH5k-6nNt-4cSv1vPB80nq2BZCzhFVR5O4VznYbsX0wZmow@mail.gmail.com