wayland/layershell: refactor layer shell surface integration

In addition to the much needed cleanup:

- The bridge/extension type is now directly tied to the QWindow
instead of the WlrLayershell object, and is much smaller.
- Layer requests are now comitted via polish instead of for each
change individually.

src/wayland/init.cpp

@@ -7,7 +7,7 @@
 #include "../core/plugin.hpp"
 
 #ifdef QS_WAYLAND_WLR_LAYERSHELL
-#include "wlr_layershell.hpp"
+#include "wlr_layershell/wlr_layershell.hpp"
 #endif
 
 void installPlatformMenuHook(); // NOLINT(misc-use-internal-linkage)
@@ -39,7 +39,12 @@ class WaylandPlugin: public QsEnginePlugin {
 
 	void registerTypes() override {
 #ifdef QS_WAYLAND_WLR_LAYERSHELL
-		qmlRegisterType<WaylandPanelInterface>("Quickshell._WaylandOverlay", 1, 0, "PanelWindow");
+		qmlRegisterType<qs::wayland::layershell::WaylandPanelInterface>(
+		    "Quickshell._WaylandOverlay",
+		    1,
+		    0,
+		    "PanelWindow"
+		);
 
 		// If any types are defined inside a module using QML_ELEMENT then all QML_ELEMENT types
 		// will not be registered. This can be worked around with a module import which makes