qmltc: QQmlContext hierarchy for created types

(Splitted from QTBUG-91956)

• (influences JavaScript lookups - e.g. id, inherited methods)
• (basic support exists, needs URL resolution tests)
• There's also a notion of scope
• URL resolution is affected by the hierarchy (see https://codereview.qt-project.org/c/qt/qtdeclarative/+/369994 for interesting test cases)
• the to-be-introduced operator '@' must behave identically to the QQmlComponent-originated objects, same applies to Qt.resolvedUrl()