Add dont-steal-focus configuration property.

Some applications send _NET_ACTIVE_WINDOW to activate their window. EXWM
respects this message always and brings such up into focus. This might
be unintended and there should be a way to turn this off. In my case the
app is Spotify desktop client installed from Flatpak.

Fixes ch11ng/exwm#732

Author: sarg

exwm-manage.el

@@ -98,6 +98,7 @@ want to match against EXWM internal variables such as `exwm-title',
                          (alist :key-type (key-sequence :tag "From")
                                 :value-type (key-sequence :tag "To")))
                         ((const :tag "Workspace" workspace) integer)
+                        ((const :tag "Don't steal focus" dont-steal-focus) boolean)
                         ((const :tag "Managed" managed) boolean)
                         ;; For forward compatibility.
                         ((other) sexp))))

exwm.el

@@ -494,16 +494,17 @@ DATA contains unmarshalled PropertyNotify event data."
     (if (buffer-live-p buffer)
         ;; Either an `exwm-mode' buffer (an X window) or a floating frame.
         (with-current-buffer buffer
-          (when (eq exwm--frame exwm-workspace--current)
-            (if exwm--floating-frame
-                (select-frame exwm--floating-frame)
-              (setq window (get-buffer-window nil t))
-              (unless window
-                ;; State change: iconic => normal.
-                (setq window (frame-selected-window exwm--frame))
-                (set-window-buffer window (current-buffer)))
-              ;; Focus transfer.
-              (select-window window))))
+          (unless (plist-get exwm--configurations 'dont-steal-focus)
+            (when (eq exwm--frame exwm-workspace--current)
+              (if exwm--floating-frame
+                  (select-frame exwm--floating-frame)
+                (setq window (get-buffer-window nil t))
+                (unless window
+                  ;; State change: iconic => normal.
+                  (setq window (frame-selected-window exwm--frame))
+                  (set-window-buffer window (current-buffer)))
+                ;; Focus transfer.
+                (select-window window)))))
       ;; A workspace.
       (dolist (f exwm-workspace--list)
         (when (eq id (frame-parameter f 'exwm-outer-id))