gdbus, win32: move most W32 dbus autolaunch code to gdbusprivate

This allows referencig them from more than single .c file.

Implementation moved without changes
from gdbusaddress.c to gdbusprivate.c

g_win32_run_session_bus signature also kept, so ABI unchanged.

gio/gdbusprivate.h

@@ -109,6 +109,16 @@ gchar *_g_dbus_hexdump (const gchar *data, gsize len, guint indent);
 
 #ifdef G_OS_WIN32
 gchar *_g_dbus_win32_get_user_sid (void);
+
+/* The g_win32_run_session_bus is exported from libgio dll on win32,
+ * but still is NOT part of API/ABI since it is declared in private header
+ * and used only by tool built from same sources.
+ * Initially this function was introduces for usage with rundll,
+ * so the signature is kept rundll-compatible, though parameters aren't used.
+ */
+__declspec(dllexport) void __stdcall
+g_win32_run_session_bus (void* hwnd, void* hinst, const char* cmdline, int cmdshow);
+gchar *_g_dbus_win32_get_session_address_dbus_launch (GError **error);
 #endif
 
 gchar *_g_dbus_get_machine_id (GError **error);