fix: depend on libxkbcommon in qtbase and kwin

qtbase configured with QT_FEATURE_xkbcommon=OFF because libxkbcommon was
never staged into its sysroot -- the recipe existed but nothing depended
on it. With the feature off, qtbase does not install
QtGui/private/qxkbcommon_p.h (src/gui/CMakeLists.txt:1095 is conditional
on it), so kwin's inputmethod.cpp failed with

    inputmethod.cpp:51: fatal error: private/qxkbcommon_p.h: No such file

kwin also includes <xkbcommon/xkbcommon-keysyms.h> directly while
declaring no such dependency, relying on it arriving transitively; that
is now explicit.

Another latent gap rather than GCC 16 fallout -- it only surfaced once
kwin compiled far enough to reach this include.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

local/recipes/kde/kwin/recipe.toml

@@ -59,6 +59,7 @@ dependencies = [
     "libudev",
     "wayland-protocols",
     "redbear-compositor",
+    "libxkbcommon",
 ]
 script = """
 DYNAMIC_INIT

local/recipes/qt/qtbase/recipe.toml

@@ -27,6 +27,9 @@ dependencies = [
     "dbus",
     "mesa",
     "openssl3",
+    # Gates QT_FEATURE_xkbcommon. Without it qtbase never installs
+    # QtGui/private/qxkbcommon_p.h, which kwin's inputmethod.cpp includes.
+    "libxkbcommon",
 ]
 script = """
 DYNAMIC_INIT