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>

src/backend/KWinInputMethod.cpp

@@ -1,6 +1,8 @@
 #include "KWinInputMethod.h"
 #include "KWinInputContext.h"
 
+#include <xkbcommon/xkbcommon-keysyms.h>
+
 KWinInputMethodGlobal::KWinInputMethodGlobal()
     : QWaylandClientExtensionTemplate(1)
 {
@@ -46,12 +48,20 @@ void KWinInputMethod::commitText(const QString &text)
 {
     if (m_context)
         m_context->commit(text);
+    else
+        m_fakeInput.typeText(text);
 }
 
 void KWinInputMethod::replaceBeforeCursor(const QString &before, const QString &text)
 {
-    if (m_context)
+    if (m_context) {
         m_context->replaceBeforeCursor(before, text);
+        return;
+    }
+    // Key events are one ordered stream, so plain Backspaces are safe here.
+    for (qsizetype i = 0; i < before.toUcs4().size(); ++i)
+        m_fakeInput.sendKeysym(XKB_KEY_BackSpace);
+    m_fakeInput.typeText(text);
 }
 
 void KWinInputMethod::setPreedit(const QString &text)
@@ -64,6 +74,8 @@ void KWinInputMethod::sendKeysym(quint32 keysym, Qt::KeyboardModifiers modifiers
 {
     if (m_context)
         m_context->sendKeysym(keysym, modifiers);
+    else
+        m_fakeInput.sendKeysym(keysym, modifiers);
 }
 
 void KWinInputMethod::activate(::zwp_input_method_context_v1 *context)