Support for casting of OpenQASM 3.0 types

[burgholzer]

The new OpenQASM standard introduces many additional datatypes besides quantum and classical registers. This allows to describe classical components of quantum algorithms in a very intuitive way. As a first step, support for all kinds of new types should be added to the QFR library and, correspondingly, to the QuantumComputation class. For details on all the new typed provided by the standard, see https://qiskit.github.io/openqasm/language/classical.html.

The standard provides the means for converting between the available types. For details, see https://qiskit.github.io/openqasm/language/types.html#casting-specifics.

This depends on #30 for the availability of all the types.