WaylandBackend: Fix relative pointer state tracking

Fix two issues with tracking state related to relative pointer mode:

* m_bPointerLocked is currently only unset through the unlock event
  handler. However, it is observed that when the locked pointer
  object is destroyed, this event is not received while the unlock
  occurs. Therefore, directly unset it when destroying the locked
  pointer object.

  This fixes the cursor staying hidden forever after rotating the
  camera using the mouse in World of Warcraft.

* When setting relative mode, m_pLockedSurface is currently compared
  against the target surface to avoid recreating the locked pointer
  object on every frame. However, m_pLockedSurface is never set so
  the code thinks we are setting relative mode on a different surface
  each frame, causing a new locked pointer object to be created
  each time.

  Fix this by setting and unsetting m_pLockedSurface when a pointer
  lock is created or destroyed.

Author: cyndis

src/Backends/WaylandBackend.cpp

@@ -2414,9 +2414,12 @@ namespace gamescope
 
                 zwp_locked_pointer_v1_destroy( m_pLockedPointer );
                 m_pLockedPointer = nullptr;
+                m_bPointerLocked = false;
 
                 zwp_relative_pointer_v1_destroy( m_pRelativePointer );
                 m_pRelativePointer = nullptr;
+
+                m_pLockedSurface = nullptr;
             }
 
 			if ( bRelative )
@@ -2425,6 +2428,8 @@ namespace gamescope
 				zwp_locked_pointer_v1_add_listener( m_pLockedPointer, &s_LockedPointerListener, this );
 
 				m_pRelativePointer = zwp_relative_pointer_manager_v1_get_relative_pointer( m_pRelativePointerManager, m_pPointer );
+
+				m_pLockedSurface = pSurface;
 			}
 
             m_InputThread.SetRelativePointer( bRelative );