PR guile/17177

PR guile/17177

	* guile/lib/gdb.scm (pretty-printers): Export.
	(set-pretty-printers!): Export.
	* guile/lib/gdb/printing.scm (gdb module): Update.
	(prepend-pretty-printer!, append-pretty-printer!): Update.
	* guile/scm-pretty-print.c (pretty_printer_list_name): Delete.
	(pretty_printer_list_var): Delete.
	(pretty_printer_list): New static global.
	(gdbscm_pretty_printers): New function.
	(gdbscm_set_pretty_printers_x): New function.
	(ppscm_find_pretty_printer_from_gdb): Update.
	(pretty_printer_functions): Add pretty-printers, set-pretty-printers!.
	(gdbscm_initialize_pretty_printers): Update.

	doc/
	* guile.texi (Guile Pretty Printing API): Fix typo.
	Document set-pretty-printers!, pretty-printers.
	(Selecting Guile Pretty-Printers): Update.
	Mention program-space based pretty-printers.