Only apply MCMT plugin on MCMTGate

[Cryoris]

Summary

Fixes #13563, by enabling the high-level synthesis plugins of MCMT only for the MCMTGate, not any gate called "mcmt".

Details and comments

While we often let it be the user's responsibility to be mindful with gate names, this is a special case as we provide a circuit called "mcmt". This can cause innocent-looking code to break, so we should add this check at least until the MCMT circuit is removed 🙂

[qiskit-bot]

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

• @Cryoris
• @Qiskit/terra-core
• @ajavadia

[coveralls]

Pull Request Test Coverage Report for Build 12465784214

Details

• 4 of 6 (66.67%) changed or added relevant lines in 1 file are covered.
• 17 unchanged lines in 3 files lost coverage.
• Overall coverage decreased (-0.007%) to 88.944%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
qiskit/transpiler/passes/synthesis/hls_plugins.py	4	6	66.67%

Files with Coverage Reduction	New Missed Lines	%
crates/accelerate/src/unitary_synthesis.rs	1	92.2%
crates/qasm2/src/lex.rs	4	91.98%
crates/qasm2/src/parse.rs	12	97.15%

Totals
Change from base Build 12420636821:	-0.007%
Covered Lines:	79426
Relevant Lines:	89299

---

💛 - Coveralls