[AlwaysOnTop] Proof of concept (#14360)

Co-authored-by: Niels Laute <niels.laute@live.nl>

src/modules/alwaysontop/AlwaysOnTop/SettingsObserver.h

@@ -0,0 +1,31 @@
+#pragma once
+
+#include <unordered_set>
+
+#include <Settings.h>
+#include <SettingsConstants.h>
+
+class SettingsObserver
+{
+public:
+    SettingsObserver(std::unordered_set<SettingId> observedSettings) :
+        m_observedSettings(std::move(observedSettings))
+    {
+        AlwaysOnTopSettings::instance().AddObserver(*this);
+    }
+
+    virtual ~SettingsObserver()
+    {
+        AlwaysOnTopSettings::instance().RemoveObserver(*this);
+    }
+
+    virtual void SettingsUpdate(SettingId type) {}
+
+    bool WantsToBeNotified(SettingId type) const noexcept 
+    {
+        return m_observedSettings.contains(type);
+    }
+
+protected:
+    std::unordered_set<SettingId> m_observedSettings;
+};