gh-142037: Improve error messages for printf-style formatting (GH-142081)

gh-142037: Improve error messages for printf-style formatting (GH-142081)

This affects string formatting as well as bytes and bytearray formatting.

* For errors in the format string, always include the position of the
  start of the format unit.
* For errors related to the formatted arguments, always include the number
  or the name of the formatted argument.
* Suggest more probable causes of errors in the format string (stray %,
  unsupported format, unexpected character).
* Provide more information when the number of arguments does not match
  the number of format units.
* Raise more specific errors when access of arguments by name is mixed with
  sequential access and when * is used with a mapping.
* Add tests for some uncovered cases.