Utils: Introduce variantFromStore and storeFromVariant

These are functional replacements for
  QVariant::fromValue(QVariantMap) (or QVariant::fromValue(Store)) and
  QVariant::toMap() (or QVariant::toValue<Store>())

We will have a few code paths in the end that need to explicitly
operarate on both QVariantMap and Store (e.g. actual reading/writing
to keep format compatibility etc), so these can't in the end be
simple to/fromValue(OneType) but need an internal 'if' or such.

Change-Id: I954f3cb24fa8fe123162b72bbd25d891dd19b768
Reviewed-by: Marcus Tillmanns <marcus.tillmanns@qt.io>

src/libs/utils/store.cpp

@@ -17,4 +17,14 @@ QStringList stringsFromKeys(const KeyList &list)
     return transform(list, &stringFromKey);
 }
 
+QVariant variantFromStore(const Store &store)
+{
+    return QVariant::fromValue(store);
+}
+
+Store storeFromVariant(const QVariant &value)
+{
+    return value.value<Store>();
+}
+
 } // Utils