Type into any window: fake input when no text field is focused

- KWinFakeInput (org_kde_kwin_fake_input v6, offered by KWin to the
  input-method process): keysyms with real modifier keys held
- The KWin backend uses the input method in text fields and fake input
  everywhere else, so shortcuts, terminals and the desktop get keys
- Text rules (auto-capitalization, double-space) only apply in fields
- Always Show setting keeps the keyboard up without a text field

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/tst_visibility.cpp

@@ -27,6 +27,18 @@ private Q_SLOTS:
         QVERIFY(v.isVisible());
     }
 
+    void alwaysVisibleShowsWithoutField()
+    {
+        VisibilityController v;
+        v.setAlwaysVisible(true);
+        QVERIFY(v.isVisible());
+        v.hide(); // dismiss key still works...
+        QVERIFY(!v.isVisible());
+        v.setFieldActive(true); // ...until the focus changes
+        v.setFieldActive(false);
+        QVERIFY(v.isVisible());
+    }
+
     void toggleShowsWithoutField()
     {
         VisibilityController v;