Temporary fix for q{i} mapping

[csookim]

The name of the ith hardware qubit is stored at index i in QibolabBackend.qubits. When passed to current qibo implementation, this is then converted to q{i} and stored in initial_layout.

This PR ensures that the keys in initial_layout (the hardware qubit names) are sorted during default transpilation, so i in gate.qubits in transpiled circuit consistently refers to the ith hardware qubit.

Will be deprecated after #1500.

Checklist:

• Reviewers confirm new code works as expected.
• Tests are passing.
• Coverage does not decrease.
• Documentation is updated.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.72%. Comparing base (05b57e9) to head (607e773).
Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1514   +/-   ##
=======================================
  Coverage   99.72%   99.72%           
=======================================
  Files          80       80           
  Lines       11781    11783    +2     
=======================================
+ Hits        11749    11751    +2     
  Misses         32       32           

Flag	Coverage Δ
unittests	99.72% <100.00%> (+<0.01%)	⬆️

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[csookim]

For completeness, there are other places where sorting initial_layout is needed. However, initial_layout will be deprecated and these changes might conflict with #1500.

For now, this fix is enough for circuit execution using the default transpiler.