Rework pg_input_error_message(), now renamed pg_input_error_info()

Rework pg_input_error_message(), now renamed pg_input_error_info()

pg_input_error_info() is now a SQL function able to return a row with
more than just the error message generated for incorrect data type
inputs when these are able to handle soft failures, returning more
contents of ErrorData, as of:
- The error message (same as before).
- The error detail, if set.
- The error hint, if set.
- SQL error code.

All the regression tests that relied on pg_input_error_message() are
updated to reflect the effects of the rename.

Per discussion with Tom Lane and Andrew Dunstan.

Author: Nathan Bossart
Discussion: https://postgr.es/m/139a68e1-bd1f-a9a7-b5fe-0be9845c6311@dunslane.net