Return correct hit-test values for title bar buttons on Windows (#4994)

Co-authored-by: Rasmus Karlsson <rasmus.karlsson@pajlada.com>

src/widgets/helper/TitlebarButtons.hpp

@@ -0,0 +1,69 @@
+#pragma once
+
+class QPoint;
+class QWidget;
+
+#include <QtGlobal>
+
+namespace chatterino {
+
+#ifdef USEWINSDK
+
+class TitleBarButton;
+class TitleBarButtons : QObject
+{
+public:
+    /// The parent of this object is set to `window`.
+    ///
+    /// All parameters must have a parent;
+    /// they're not deleted in the destructor.
+    TitleBarButtons(QWidget *window, TitleBarButton *minButton,
+                    TitleBarButton *maxButton, TitleBarButton *closeButton);
+
+    /// Hover over the button `ht` at the global position `at`.
+    ///
+    /// @pre `ht` must be one of { HTMAXBUTTON, HTMINBUTTON, HTCLOSE }.
+    /// @param ht The hovered button
+    /// @param at The global position of the event
+    void hover(size_t ht, QPoint at);
+
+    /// Leave all buttons - simulate `leaveEvent` for all buttons.
+    void leave();
+
+    /// Press the left mouse over the button `ht` at the global position `at`.
+    ///
+    /// @pre `ht` must be one of { HTMAXBUTTON, HTMINBUTTON, HTCLOSE }.
+    /// @param ht The clicked button
+    /// @param at The global position of the event
+    void mousePress(size_t ht, QPoint at);
+
+    /// Release the left mouse button over the button `ht` at the
+    /// global position `at`.
+    ///
+    /// @pre `ht` must be one of { HTMAXBUTTON, HTMINBUTTON, HTCLOSE }.
+    /// @param ht The clicked button
+    /// @param at The global position of the event
+    void mouseRelease(size_t ht, QPoint at);
+
+    /// Update the maximize/restore button to show the correct image
+    /// according to the current window state.
+    void updateMaxButton();
+
+    /// Set buttons to be narrow.
+    void setSmallSize();
+    /// Set buttons to be regular size.
+    void setRegularSize();
+
+private:
+    /// @pre ht must be one of { HTMAXBUTTON, HTMINBUTTON, HTCLOSE }.
+    TitleBarButton *buttonForHt(size_t ht) const;
+
+    QWidget *window_ = nullptr;
+    TitleBarButton *minButton_ = nullptr;
+    TitleBarButton *maxButton_ = nullptr;
+    TitleBarButton *closeButton_ = nullptr;
+};
+
+#endif
+
+}  // namespace chatterino