Core/Utils: Migrate further to Utils::Id

The coreplugin/id.h header is kept for downstream for now.

Change-Id: I8c44590f7b988b3770ecdc177c40783e12353e66
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/plugins/cpptools/modelmanagertesthelper.cpp

@@ -41,7 +41,7 @@ TestProject::TestProject(const QString &name, QObject *parent) :
     m_name(name)
 {
     setParent(parent);
-    setId(Core::Id::fromString(name));
+    setId(Utils::Id::fromString(name));
     setDisplayName(name);
     qRegisterMetaType<QSet<QString> >();
 }