Revert "Close popup window when focus is lost (case 1258571) (#1907)"

This reverts commit a60bb69.

Author: sebastienlagarde

com.unity.render-pipelines.core/Editor/FilterWindow.cs

@@ -232,8 +232,6 @@ void OnDisable()
             s_FilterWindow = null;
         }
 
-        void OnLostFocus() => Close();
-
         internal static bool ValidateAddComponentMenuItem()
         {
             return true;

com.unity.render-pipelines.high-definition/CHANGELOG.md

@@ -89,7 +89,6 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Force probe to render again if first time was during async shader compilation to avoid having cyan objects.
 - Fixed for lookdev library field not being refreshed upon opening a library from the environment library inspector.
 - Fixed serialization issue with matcap scale intensity.
-- Close Add Override popup of Volume Inspector when the popup looses focus (case 1258571)
 
 ### Changed
 - Preparation pass for RTSSShadows to be supported by render graph.