Use WM_WINDOW_ROLE instead of WM_STATE to detect the host window

Ardour brings up the plugin UI before the host window is visible, and it
is missing some properties. Using WM_WINDOW_ROLE instead of WM_STATE
makes it work.

For reference, these are the properties that are set on the window at
the time of plugin GUI instantiation:

_NET_WM_ICON(CARDINAL) =        Icon (16 x 16):
WM_WINDOW_ROLE(STRING) = "plugin_ui"
_NET_WM_SYNC_REQUEST_COUNTER(CARDINAL) = 6294918
_NET_WM_WINDOW_TYPE(ATOM) = _NET_WM_WINDOW_TYPE_UTILITY
_NET_WM_USER_TIME_WINDOW(WINDOW): window id # 0x600d85
WM_CLIENT_LEADER(WINDOW): window id # 0x600001
_NET_WM_PID(CARDINAL) = 1604801
WM_LOCALE_NAME(STRING) = "en_US.UTF-8"
WM_CLIENT_MACHINE(STRING) = "homura"
WM_NORMAL_HINTS(WM_SIZE_HINTS):
                program specified size: 521 by 46
WM_PROTOCOLS(ATOM): protocols  WM_DELETE_WINDOW, WM_TAKE_FOCUS, _NET_WM_PING, _NET_WM_SYNC_REQUEST
WM_CLASS(STRING) = "ardour-8.12.0", "Ardour-8.12.0"
WM_ICON_NAME(STRING) = "Audio 1: Melodyne (by Celemony) [VST3]"
_NET_WM_ICON_NAME(UTF8_STRING) = "Audio 1: Melodyne (by Celemony) [VST3]"
WM_NAME(STRING) = "Audio 1: Melodyne (by Celemony) [VST3]"
_NET_WM_NAME(UTF8_STRING) = "Audio 1: Melodyne (by Celemony) [VST3]"

src/wine-host/editor.h

@@ -374,6 +374,11 @@ class Editor {
      */
     xcb_atom_t xcb_wm_state_property_;
 
+    /**
+     * The atom corresponding to `WM_WINDOW_ROLE`.
+     */
+    xcb_atom_t xcb_wm_window_role_property_;
+
     /**
      * The window handle of the editor window created by the DAW.
      */