Advance redbear-full Wayland, greeter, and Qt integration

Consolidate the active desktop path around redbear-full while landing the greeter/session stack and the runtime fixes needed to keep Wayland and KWin bring-up moving forward.

local/recipes/system/redbear-greeter/source/ui/main.cpp

@@ -0,0 +1,25 @@
+#include <QGuiApplication>
+#include <QQmlApplicationEngine>
+#include <QQmlContext>
+#include <QQuickStyle>
+
+#include "greeter_backend.h"
+
+int main(int argc, char *argv[]) {
+    qputenv("QT_QUICK_CONTROLS_STYLE", QByteArrayLiteral("Basic"));
+
+    QGuiApplication app(argc, argv);
+    QQuickStyle::setStyle(QStringLiteral("Basic"));
+
+    GreeterBackend backend;
+    QQmlApplicationEngine engine;
+    engine.rootContext()->setContextProperty(QStringLiteral("greeterBackend"), &backend);
+    engine.load(QUrl(QStringLiteral("qrc:/Main.qml")));
+
+    if (engine.rootObjects().isEmpty()) {
+        return 1;
+    }
+
+    backend.initialize();
+    return app.exec();
+}