Change supported platforms of kglobalaccel plugin to "org.kde.kwin"

Overwrite the platform name through the environment variable and ensure
that the plugin is not picked in non-kwin Wayland sessions as that puts
kglobalaccel5 into a crash restart loop.

BUG: 349911

globalshortcuts.cpp

@@ -115,6 +115,7 @@ GlobalShortcutsManager::~GlobalShortcutsManager()
 void GlobalShortcutsManager::init()
 {
     if (kwinApp()->shouldUseWaylandForCompositing()) {
+        qputenv("KGLOBALACCELD_PLATFORM", QByteArrayLiteral("org.kde.kwin"));
         m_kglobalAccel = new KGlobalAccelD(this);
         if (!m_kglobalAccel->init()) {
             qCDebug(KWIN_CORE) << "Init of kglobalaccel failed";

plugins/kglobalaccel/kwin.json

@@ -1,3 +1,3 @@
 {
-    "platforms": ["wayland", "wayland-egl"]
+    "platforms": ["org.kde.kwin"]
 }