Deprecate qpy loading of old library pulses with complex amp

[TsafrirA]

Summary

This PR completes #10357 and adds a deprecation warning when loading an old QPY file containing library symbolic pulses with complex amp.

Details and comments

The deprecation process began in #9002, but #10357 neglected to promote this specific warning to a deprecation warning. The PR is meant for 0.46, while 1.0.0 will have the support removed.

[qiskit-bot]

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

• @Qiskit/terra-core
• @mtreinish
• @nkanazawa1989

[ElePT]

LGTM! I take that the next step will be the removal PR against main. Thanks for following through with the slightly annoying deprecation procedure :)

[ElePT]

I just realized that the stacklevel of the deprecation warning is not set (it defaults to 1), which means that the message will not be seen unless a user explicitly calls _read_symbolic_pulse (which is unlikely). The level should match the number of function calls that happen between qpy.load and _read_symbolic_pulse, and this is actually kind of tricky in this case, because it's not a fixed number. I will bring it up to the team and think of a solution.

[ElePT]

Even though #11260 isn't merged yet, I will go ahead and add this PR to the merge queue, and take care of changing the warning class of loading complex amp. as part of #11260. This will also let us double check that the warning is raised properly as part of the PR that introduces the new warning class, which I think makes sense.