doc: Fix descriptions related to the handling of non-ASCII characters
Since
45b1a67a0fcb, non-printable ASCII characters do not show up in
various configuration paths as question marks, but as hexadecimal
escapes. The documentation was not updated to reflect that.
Author: Hayato Kuroda
Reviewed-by: Jian He, Tom Lane, Karl O. Pinc, Peter Smith
Discussion: https://postgr.es/m/TYAPR01MB586631D0961BF9C44893FAB1F523A@TYAPR01MB5866.jpnprd01.prod.outlook.com
Backpatch-through: 16