Fix string type name in qmllint

The "length" property is special cased because it's the only own
property of any JavaScript built-in type. As we've changed the internal
name of the string type in builtins.qmltypes, we need to reflect this in
qmllint.

Fixes: QTBUG-92447
Pick-to: 6.0 6.1
Change-Id: I9a5c7e9ab3da686bb6ac3fdffa36269abb0eb6ea
Reviewed-by: Maximilian Goldstein <max.goldstein@qt.io>
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

tests/auto/qml/qmllint/data/stringLength.qml

@@ -0,0 +1,9 @@
+import QtQuick 2.15
+
+TextInput {
+    id: textInput
+
+    Component.onCompleted: {
+        console.log("text.length", textInput.text.length);
+    }
+}

tests/auto/qml/qmllint/tst_qmllint.cpp

@@ -620,6 +620,7 @@ void TestQmllint::cleanQmlCode_data()
     QTest::newRow("Used imports") << QStringLiteral("used.qml");
     QTest::newRow("Unused imports (multi)") << QStringLiteral("unused_multi.qml");
     QTest::newRow("compositeSingleton") << QStringLiteral("compositesingleton.qml");
+    QTest::newRow("stringLength") << QStringLiteral("stringLength.qml");
 }
 
 void TestQmllint::cleanQmlCode()

tools/qmllint/checkidentifiers.cpp

@@ -124,7 +124,7 @@ void CheckIdentifiers::checkMemberAccess(const QVector<FieldMember> &members,
                 continue;
             }
 
-            if (typeName == QLatin1String("string")) {
+            if (typeName == QLatin1String("QString")) {
                 detectedRestrictiveKind = typeName;
                 detectedRestrictiveName = access.m_name;
                 expectedNext.append(QLatin1String("length"));