Include QVariantPair in documentation of QMetaType::Type

When it was added, along with the type it describes, it wasn't added
to the QDoc-only fake version of Type's declaration, or to the \enum's
list of \value entries. There being no clear reason for those
omissions, I'm presuming to guess they were just an oversight.

This amends commit c7ce1bc05c which was
included in Qt 6.0.0.

Pick-to: 6.2 6.4
Change-Id: I1bf9fe0f0a31219a888666550a197e479d8eadc1
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/kernel/qmetatype.cpp

@@ -371,6 +371,7 @@ const char *QtMetaTypePrivate::typedefNameForType(const QtPrivate::QMetaTypeInte
     \value QStringList QStringList
     \value QVariantMap QVariantMap
     \value QVariantHash QVariantHash
+    \value QVariantPair QVariantPair
     \value QIcon QIcon
     \value QPen QPen
     \value QLineF QLineF

src/corelib/kernel/qmetatype.h

@@ -344,7 +344,7 @@ public:
         QByteArrayList = 49, QObjectStar = 39, SChar = 40,
         Void = 43,
         Nullptr = 51,
-        QVariantMap = 8, QVariantList = 9, QVariantHash = 28,
+        QVariantMap = 8, QVariantList = 9, QVariantHash = 28, QVariantPair = 58,
         QCborSimpleType = 52, QCborValue = 53, QCborArray = 54, QCborMap = 55,
         Char16 = 56, Char32 = 57,