Add (state) Schmidt decomposition to quantum_info.linalg_operations

[renatomello]

This is the first step to close #1345. However, fully closing it requires implementing the Schmidt decomposition for operators.

EDIT: Needs #1473

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 99.93%. Comparing base (e7276d8) to head (b7f0de3).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1471   +/-   ##
=======================================
  Coverage   99.93%   99.93%           
=======================================
  Files          81       81           
  Lines       11795    11805   +10     
=======================================
+ Hits        11787    11797   +10     
  Misses          8        8           

Flag	Coverage Δ
unittests	99.93% <100.00%> (+<0.01%)	⬆️

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[renatomello]

@Simone-Bordoni I'm using this function to replace another one in the transpiler, so could you please check that everything is ok? Thanks.

[Simone-Bordoni]

@Simone-Bordoni I'm using this function to replace another one in the transpiler, so could you please check that everything is ok? Thanks.

Much better now! Hopefully it should also improve the precision in the different backends.