Fix qft-plugins for custom 'qft' gates (backport #13181)

[mergify]

Summary

The HighLevelSynthesis transpiler pass no longer raises an exception when encountering a custom gate that is called "qft" but is not an instance of class QFTGate. Instead, the synthesis plugins for QFT gates ignore such a gate, and the gate's definition is used (if provided).

Fixes #13120 and #13174.

The PR is very short and has backport potential (if desired).

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This is an automatic backport of pull request #13181 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 2245a4f has failed:

On branch mergify/bp/stable/1.2/pr-13181
Your branch is up to date with 'origin/stable/1.2'.

You are currently cherry-picking commit 2245a4f44.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	new file:   releasenotes/notes/fix-qft-plugins-7106029d33c44b96.yaml

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	deleted by us:   qiskit/transpiler/passes/synthesis/hls_plugins.py
	both modified:   test/python/transpiler/test_high_level_synthesis.py

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[qiskit-bot]

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One or more of the following people are relevant to this code:

• @Qiskit/terra-core

[jakelishman]

Assuming this passes lint/tests, it should now be a clean cherry-pick.

[coveralls]

Pull Request Test Coverage Report for Build 10945733297

Details

• 2 of 2 (100.0%) changed or added relevant lines in 1 file are covered.
• 17 unchanged lines in 2 files lost coverage.
• Overall coverage remained the same at 89.758%

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Files with Coverage Reduction	New Missed Lines	%
crates/qasm2/src/lex.rs	5	91.73%
crates/qasm2/src/parse.rs	12	97.15%

Totals
Change from base Build 10938909061:	0.0%
Covered Lines:	66873
Relevant Lines:	74504

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💛 - Coveralls