feat(wayland): create cross platform window interfaces

Internally this also refactors a ton of code around the wayland
layershell. Note that attachment failures are still broken and
platform interfaces are hardcoded.

src/core/floatingwindow.hpp

@@ -0,0 +1,56 @@
+#pragma once
+
+#include <qobject.h>
+#include <qtmetamacros.h>
+
+#include "proxywindow.hpp"
+
+class ProxyFloatingWindow: public ProxyWindowBase {
+	Q_OBJECT;
+
+public:
+	explicit ProxyFloatingWindow(QObject* parent = nullptr): ProxyWindowBase(parent) {}
+
+	// Setting geometry while the window is visible makes the content item shrinks but not the window
+	// which is awful so we disable it for floating windows.
+	void setWidth(qint32 width) override;
+	void setHeight(qint32 height) override;
+};
+
+///! Standard floating window.
+class FloatingWindowInterface: public WindowInterface {
+	Q_OBJECT;
+	QML_NAMED_ELEMENT(FloatingWindow);
+
+public:
+	explicit FloatingWindowInterface(QObject* parent = nullptr);
+
+	void onReload(QObject* oldInstance) override;
+
+	[[nodiscard]] QQuickItem* contentItem() const override;
+
+	// NOLINTBEGIN
+	[[nodiscard]] bool isVisible() const override;
+	void setVisible(bool visible) override;
+
+	[[nodiscard]] qint32 width() const override;
+	void setWidth(qint32 width) override;
+
+	[[nodiscard]] qint32 height() const override;
+	void setHeight(qint32 height) override;
+
+	[[nodiscard]] QuickShellScreenInfo* screen() const override;
+	void setScreen(QuickShellScreenInfo* screen) override;
+
+	[[nodiscard]] QColor color() const override;
+	void setColor(QColor color) override;
+
+	[[nodiscard]] PendingRegion* mask() const override;
+	void setMask(PendingRegion* mask) override;
+
+	[[nodiscard]] QQmlListProperty<QObject> data() override;
+	// NOLINTEND
+
+private:
+	ProxyFloatingWindow* window;
+};