Hold Keys mode: keys stay down while touched, like a hardware keyboard

- HardwareKeys presses a key's unshifted keysym on touch and releases it
  on lift, through fake input; held keys repeat and combine as on a
  physical keyboard (games, Shift+click)
- Shift/Ctrl/Alt/Super are plain held keys, caps lock is the system's,
  dead keys compose in the app
- No long-press, flick, trackpad or rollover in this mode; nothing is
  left held when the mode is turned off or touches are cancelled
- Settings switch; default stays the touch (virtual keyboard) mode

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

src/backend/KWinInputMethod.cpp

@@ -78,6 +78,13 @@ void KWinInputMethod::sendKeysym(quint32 keysym, Qt::KeyboardModifiers modifiers
         m_fakeInput.sendKeysym(keysym, modifiers);
 }
 
+// Always fake input, even in a text field: held keys are key events, and the
+// input method's keysyms can't hold a modifier across keys.
+void KWinInputMethod::setKeyPressed(quint32 keysym, bool pressed)
+{
+    m_fakeInput.setKeyPressed(keysym, pressed);
+}
+
 void KWinInputMethod::activate(::zwp_input_method_context_v1 *context)
 {
     m_context = std::make_unique<KWinInputContext>(context);