Fixing bug in single-qubit gate adjusting in HeuristicMapper

[EliasLF]

Description

The changed line previously treated qc::QuantumComputation::initialLayout as a mapping from virtual qubits to physical qubits instead of the other way around, which seems to be the canonical way everywhere else in the project. This leads to invalid qubit layouts in some edge cases (i.e. non-bijective mappings)

Checklist:

• The pull request only contains commits that are related to it.
• I have added appropriate tests and documentation.
• I have made sure that all CI jobs on GitHub pass.
• The pull request introduces no new warnings and follows the project's style guidelines.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (ec8d036) 93.0% compared to head (7d6ef95) 93.1%.

Additional details and impacted files

@@           Coverage Diff           @@
##            main    #408     +/-   ##
=======================================
+ Coverage   93.0%   93.1%   +0.1%     
=======================================
  Files         46      46             
  Lines       4895    4895             
  Branches     849     849             
=======================================
+ Hits        4554    4559      +5     
+ Misses       341     336      -5     

Flag	Coverage Δ
cpp	92.8% <100.0%> (+0.1%)	⬆️
python	96.0% <ø> (ø)

Files	Coverage Δ
src/heuristic/HeuristicMapper.cpp	94.1% <100.0%> (+0.1%)	⬆️

... and 1 file with indirect coverage changes

[burgholzer]

Lgtm 👍🏻 thanks for catching this!