Add some missing properties to Deleted

Summary:
### keepAbove

Some effects(e.g. Dim Inactive) can take keep above state of a window
into account when they are making decision whether to operate on it.
Because Deleted doesn't expose keepAbove property, it will be always
`true`, which is wrong.

### keepBelow

This property was added as a counterpart to keepAbove.

### caption

That's mostly for debugging purposes, e.g.

```lang=cpp
void CoolEffect::windowClosed(EffectWindow *w)
{
    qDebug() << w->caption() << "has been closed";
    qDebug() << "keep above:" << w->keepAbove();
}
```

Test Plan: Manually.

Reviewers: #kwin, davidedmundson

Reviewed By: #kwin, davidedmundson

Subscribers: kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D13649

deleted.cpp

@@ -44,6 +44,8 @@ Deleted::Deleted()
     , m_wasCurrentTab(true)
     , m_decorationRenderer(nullptr)
     , m_fullscreen(false)
+    , m_keepAbove(false)
+    , m_keepBelow(false)
 {
 }
 
@@ -112,6 +114,9 @@ void Deleted::copyToDeleted(Toplevel* c)
         }
         m_fullscreen = client->isFullScreen();
         m_wasCurrentTab = client->isCurrentTab();
+        m_keepAbove = client->keepAbove();
+        m_keepBelow = client->keepBelow();
+        m_caption = client->caption();
     }
 }
 

deleted.h

@@ -41,6 +41,9 @@ class KWIN_EXPORT Deleted
     Q_PROPERTY(bool modal READ isModal)
     Q_PROPERTY(bool fullScreen READ isFullScreen CONSTANT)
     Q_PROPERTY(bool isCurrentTab READ isCurrentTab)
+    Q_PROPERTY(bool keepAbove READ keepAbove CONSTANT)
+    Q_PROPERTY(bool keepBelow READ keepBelow CONSTANT)
+    Q_PROPERTY(QString caption READ caption CONSTANT)
 public:
     static Deleted* create(Toplevel* c);
     // used by effects to keep the window around for e.g. fadeout effects when it's destroyed
@@ -92,6 +95,15 @@ public:
     bool isCurrentTab() const {
         return m_wasCurrentTab;
     }
+    bool keepAbove() const {
+        return m_keepAbove;
+    }
+    bool keepBelow() const {
+        return m_keepBelow;
+    }
+    QString caption() const {
+        return m_caption;
+    }
 protected:
     virtual void debug(QDebug& stream) const;
 private Q_SLOTS:
@@ -125,6 +137,9 @@ private:
     NET::WindowType m_type = NET::Unknown;
     QByteArray m_windowRole;
     bool m_fullscreen;
+    bool m_keepAbove;
+    bool m_keepBelow;
+    QString m_caption;
 };
 
 inline void Deleted::refWindow()