dix: add getter for display name

Xrdp needs to know the current display name (for setting up it's
own server sockets accordingly). Instead of exporting an internal
field, adding a little getter for this.

Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>
Part-of: <https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/1783>

dix/display.c

@@ -0,0 +1,19 @@
+/* SPDX-License-Identifier: MIT OR X11
+ *
+ * Copyright © 2024 Enrico Weigelt, metux IT consult <info@metux.net>
+ */
+#include <dix-config.h>
+
+#include "dix/dix_priv.h"
+#include "include/dix.h"
+#include "include/screenint.h"
+
+const char *display = "0";
+int displayfd = -1;
+
+const char *dixGetDisplayName(ScreenPtr *pScreen)
+{
+    // pScreen currently is ignored as the value is global,
+    // but this might perhaps change in the future.
+    return display;
+}