ecc::Q18Surface code: phase flip correction

[pichristoph]

    How temporary is this deactivation? Something to be fixed before this PR is merged?

If not, then please create an issue for that. Otherwise I am fairly certain this will get lost.

Originally posted by @burgholzer in cda-tum/mqt-core#210 (comment)

Currently, the ecc::Q18Surface error correction code only corrects bit flips.
The basic procedure for correcting phase errors is very similar to bit flip correction, however, only the initialization of ancilla qubits takes more effort and thus still has to be done.

Strategy: Starting with the 0-state, we perform a "measure-and-correct" step. To work correctly, this step has to detect and correct multiple errors at once. In the current implementation (already used for bit flip correction), multiple errors can be detected, but only single errors can be corrected.