Make iqp the matplotlib default style

[Cryoris]

Summary

Following #10950, this PR sets "iqp" as the new default for the matplotlib drawer.

Note: Due to the apparent impossibility of reproducing the precise matplotlib drawings locally I'm abusing the CI to generate the correct images, hence, opening this early draft PR.

Details and comments

In addition, this PR includes some additional changes

• Using the black-white scheme must explicitly use style="bw" instead of style=False. This is a suggestion for a more consistent interface, the deprecation would be out into 0.46.
• Refactors the DefaultStyle to not hardcode the default colors but load it from a JSON, such as all other color schemes.
• Introduces a StyleDict, which is a dictionary handling matplotlib-specific aliases (such as "ec" for "edgecolor") instead of keeping a dictionary with duplicate entries.

[coveralls]

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• 0 of 0 changed or added relevant lines in 0 files are covered.
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• Overall coverage increased (+0.01%) to 89.361%

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Totals
Change from base Build 7503395201:	0.01%
Covered Lines:	59669
Relevant Lines:	66773

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💛 - Coveralls

[qiskit-bot]

One or more of the the following people are requested to review this:

• @enavarro51
• @Qiskit/terra-core

[ElePT]

LGTM, but there are still a few lint complains to fix. I think that the docs failures might get resolved after merging from main (at least that was the case for a PR I had with the same issues.

[jakelishman]

I think the docs failure is local to this PR - the actual errors are these:

/home/vsts/work/1/s/.tox/docs/lib/python3.9/site-packages/qiskit/circuit/quantumcircuit.py:docstring of qiskit.circuit.quantumcircuit.QuantumCircuit.draw:30: ERROR: Unexpected indentation.
/home/vsts/work/1/s/.tox/docs/lib/python3.9/site-packages/qiskit/circuit/quantumcircuit.py:docstring of qiskit.circuit.quantumcircuit.QuantumCircuit.draw:31: WARNING: Block quote ends without a blank line; unexpected unindent.
/home/vsts/work/1/s/.tox/docs/lib/python3.9/site-packages/qiskit/visualization/circuit/circuit_visualization.py:docstring of qiskit.visualization.circuit.circuit_visualization.circuit_drawer:30: ERROR: Unexpected indentation.
/home/vsts/work/1/s/.tox/docs/lib/python3.9/site-packages/qiskit/visualization/circuit/circuit_visualization.py:docstring of qiskit.visualization.circuit.circuit_visualization.circuit_drawer:31: WARNING: Block quote ends without a blank line; unexpected unindent.

They're both probably because a bullet list is starting on the first continuation line - it likely wants a blank line before (and maybe after) the start of the list in the style argument.

[ElePT]

Approving in hopes that lint passes this time :)

[ElePT]

Preliminary tests passing! I'll re-approve and hope for no further surprises.