wayland: Let user set "no border" property in more cases

It can also be applied to client-side decorations. As long as the
compositor can ask the client to use some specific decoration mode, the
"no border" property can be set.

autotests/integration/xdgshellclient_test.cpp

@@ -995,7 +995,6 @@ void TestXdgShellClient::testXdgDecoration()
 
     shellSurface->xdgSurface()->ack_configure(surfaceConfigureRequestedSpy.last()[0].toInt());
     auto c = Test::renderAndWaitForShown(surface.data(), QSize(100, 50), Qt::blue);
-    QCOMPARE(c->userCanSetNoBorder(), expectedMode == Test::XdgToplevelDecorationV1::mode_server_side);
     QCOMPARE(c->isDecorated(), expectedMode == Test::XdgToplevelDecorationV1::mode_server_side);
 }
 

src/xdgshellclient.cpp

@@ -723,26 +723,7 @@ bool XdgToplevelClient::userCanSetFullScreen() const
 
 bool XdgToplevelClient::userCanSetNoBorder() const
 {
-    if (m_serverDecoration) {
-        switch (m_serverDecoration->preferredMode()) {
-        case ServerSideDecorationManagerInterface::Mode::Server:
-            return !isFullScreen() && !isShade();
-        case ServerSideDecorationManagerInterface::Mode::Client:
-        case ServerSideDecorationManagerInterface::Mode::None:
-            return false;
-        }
-    }
-    if (m_xdgDecoration) {
-        switch (m_xdgDecoration->preferredMode()) {
-        case XdgToplevelDecorationV1Interface::Mode::Server:
-        case XdgToplevelDecorationV1Interface::Mode::Undefined:
-            return Decoration::DecorationBridge::hasPlugin() && !isFullScreen() && !isShade();
-        case XdgToplevelDecorationV1Interface::Mode::None:
-        case XdgToplevelDecorationV1Interface::Mode::Client:
-            return false;
-        }
-    }
-    return false;
+    return (m_serverDecoration || m_xdgDecoration) && !isFullScreen() && !isShade();
 }
 
 bool XdgToplevelClient::noBorder() const