bsdinstall hostname: Restore bsdconfig API

Restore bsdconfig API to handle hostname dialog because bsddialog 1.0
matches all features required by bsdconfig(1). Implicitly this commit
restores also Xdialog(1) for this script.

This commit reverts:
 - "bsdinstall hostname: Replace dialog with bsddialog"
   6368dcb292
 - "bsdinstall(8) hostname: Update for bsddialog 0.3"
   5f3ec44e7e.

The script continues to use bsddialog(1) by default via $DIALOG in
bsdconfig(1).

usr.sbin/bsdinstall/scripts/hostname

@@ -47,8 +47,6 @@ f_include $BSDCFG_SHARE/dialog.subr
 
 ############################################################ GLOBALS
 
-: ${BSDDIALOG_CANCEL=1}
-
 #
 # Strings that should be moved to an i18n file and loaded with f_include_lang()
 #
@@ -75,14 +73,18 @@ dialog_hostname()
 	local hline=
 	local value="$*"
 
-	bsddialog \
+	local height width
+	f_dialog_inputbox_size height width \
+		"$DIALOG_TITLE" "$DIALOG_BACKTITLE" "$prompt" "$value" "$hline"
+
+	$DIALOG \
 		--title "$DIALOG_TITLE"         \
 		--backtitle "$DIALOG_BACKTITLE" \
 		--hline "$hline"                \
 		--ok-label "$msg_ok"            \
 		--no-cancel                     \
 		--inputbox "$prompt"            \
-		0 0 "$value"                    \
+		$height $width "$value"         \
 		2>&1 >&$DIALOG_TERMINAL_PASSTHRU_FD
 }
 
@@ -98,7 +100,7 @@ f_dialog_backtitle "$msg_freebsd_installer"
 # Get user input
 #
 HOSTNAME=$( dialog_hostname "$HOSTNAME" )
-[ $? -eq $BSDDIALOG_CANCEL ] && exit 1
+[ $? -eq $DIALOG_CANCEL ] && exit 1
 
 #
 # Store the user's choice