Locate the debug Qt WebEngine resources under the vcpkg debug tree.

In the vcpkg layout the qtwebengine port moves the release WebEngine resources
into share/Qt6/resources (== QT_INSTALL_DATA/resources), but keeps the debug
".debug.pak" resources under <prefix>/debug/resources. QT_INSTALL_DATA is shared
between the debug and release configurations, so windeployqt looked for the debug
resources in share/Qt6/resources and failed with e.g.
    "...\share\Qt6\resources\qtwebengine_resources.debug.pak does not exist."

Resolve the resources from QT_INSTALL_PREFIX/debug for a debug deployment; the
release path is unchanged. Paired with the LibraryExecutables fix in qt.conf.in
(which points QT_INSTALL_LIBEXECS at tools/Qt6/bin/debug for the debug config),
this lets windeployqt deploy Qt WebEngine for debug builds without relocating any
debug binaries into the non-debug tree.

diff --git a/src/tools/windeployqt/main.cpp b/src/tools/windeployqt/main.cpp
index 839a0b4..bd0590e 100644
--- a/src/tools/windeployqt/main.cpp
+++ b/src/tools/windeployqt/main.cpp
@@ -1955,8 +1955,13 @@ static bool deployWebEngineCore(const QMap<QString, QString> &qtpathsVariables,
     if (!deployWebProcess(qtpathsVariables, webEngineProcessName, pluginInfo, options, errorMessage))
         return false;
     const QString resourcesSubDir = QStringLiteral("/resources");
-    const QString resourcesSourceDir = qtpathsVariables.value(QStringLiteral("QT_INSTALL_DATA"))
-            + resourcesSubDir + u'/';
+    // vcpkg keeps the debug Qt WebEngine resources (.debug.pak) under <prefix>/debug/resources,
+    // separate from the release resources in QT_INSTALL_DATA/resources. QT_INSTALL_DATA is shared
+    // between debug and release, so resolve the debug resources from the prefix instead.
+    const QString resourcesBaseDir = isDebug
+            ? qtpathsVariables.value(QStringLiteral("QT_INSTALL_PREFIX")) + QStringLiteral("/debug")
+            : qtpathsVariables.value(QStringLiteral("QT_INSTALL_DATA"));
+    const QString resourcesSourceDir = resourcesBaseDir + resourcesSubDir + u'/';
     const QString resourcesTargetDir(options.directory + resourcesSubDir);
     if (!createDirectory(resourcesTargetDir, errorMessage, options.dryRun))
         return false;