Add debug topic "session-management"

This is used to print debug information for session management.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3825>

src/core/util.c

@@ -70,6 +70,7 @@ static const GDebugKey meta_debug_keys[] = {
   { "input-events", META_DEBUG_INPUT_EVENTS },
   { "eis", META_DEBUG_EIS },
   { "kms-deadline", META_DEBUG_KMS_DEADLINE },
+  { "session-management", META_DEBUG_SESSION_MANAGEMENT },
 };
 
 static gint verbose_topics = 0;
@@ -329,6 +330,8 @@ meta_topic_to_string (MetaDebugTopic topic)
       return "EIS";
     case META_DEBUG_KMS_DEADLINE:
       return "KMS_DEADLINE";
+    case META_DEBUG_SESSION_MANAGEMENT:
+      return "SESSION_MANAGEMENT";
     }
 
   return "WM";

src/meta/meta-debug.h

@@ -51,6 +51,7 @@
  * @META_DEBUG_INPUT_EVENTS: input events
  * @META_DEBUG_EIS: eis state
  * @META_DEBUG_KMS_DEADLINE: KMS deadline timers
+ * @META_DEBUG_SESSION_MANAGEMENT: session management
  */
 typedef enum
 {
@@ -85,6 +86,7 @@ typedef enum
   META_DEBUG_INPUT_EVENTS    = 1 << 27,
   META_DEBUG_EIS             = 1 << 28,
   META_DEBUG_KMS_DEADLINE    = 1 << 29,
+  META_DEBUG_SESSION_MANAGEMENT = 1 << 30,
 } MetaDebugTopic;
 
 META_EXPORT