Move TitleBar::supportsMinimize|MaximizeButton into FloatingWindow

Just a minor refactoring so FloatingWindow can save it during serialization.
So we can support per-floating window settings.

src/private/FloatingWindow.cpp

@@ -729,3 +729,13 @@ void FloatingWindow::ensureRectIsOnScreen(QRect &geometry)
         geometry.moveBottom(scrGeom.bottom());
     }
 }
+
+bool FloatingWindow::supportsMinimizeButton() const
+{
+    return (Config::self().flags() & Config::Flag_TitleBarHasMinimizeButton) == Config::Flag_TitleBarHasMinimizeButton; // this specific flag is not base^2
+}
+
+bool FloatingWindow::supportsMaximizeButton() const
+{
+    return Config::self().flags() & Config::Flag_TitleBarHasMaximizeButton;
+}

src/private/FloatingWindow_p.h

@@ -222,6 +222,12 @@ public:
     /// be open ended
     static Qt::WindowFlags s_windowFlagsOverride;
 
+    /// @brief Returns whether this floating window supports showing a minimize button
+    bool supportsMinimizeButton() const;
+
+    /// @brief Returns whether this floating window supports showing a maximize button
+    bool supportsMaximizeButton() const;
+
 Q_SIGNALS:
     void activatedChanged();
     void numFramesChanged();

src/private/TitleBar.cpp

@@ -306,18 +306,12 @@ bool TitleBar::supportsFloatingButton() const
 
 bool TitleBar::supportsMaximizeButton() const
 {
-    if (!(Config::self().flags() & Config::Flag_TitleBarHasMaximizeButton))
-        return false;
-
-    return m_floatingWindow != nullptr;
+    return m_floatingWindow && m_floatingWindow->supportsMaximizeButton();
 }
 
 bool TitleBar::supportsMinimizeButton() const
 {
-    if ((Config::self().flags() & Config::Flag_TitleBarHasMinimizeButton) != Config::Flag_TitleBarHasMinimizeButton) // this specific flag is not base^2
-        return false;
-
-    return m_floatingWindow != nullptr;
+    return m_floatingWindow && m_floatingWindow->supportsMinimizeButton();
 }
 
 bool TitleBar::supportsAutoHideButton() const