Merge u1, u2 and p gate together if they contain parameters.

[rafal-pracht]

Summary

Before the fix, the 'Optimize1qGates' transpiler optimization join together the gate only when the parameter was bounded (or when there was no parameter at all). After the fix, the u1, u2, and p gates will be combined even when the parameter is unbounded.

from qiskit import QuantumCircuit
from qiskit.circuit import Parameter
from qiskit.transpiler import PassManager
from qiskit.transpiler.passes import Optimize1qGates, Unroller

phi = Parameter('φ')
alpha = Parameter('α')

qc = QuantumCircuit(1)
qc.u1(2*phi, 0)
qc.u1(alpha, 0)
qc.u1(0.1, 0)
qc.u1(0.2, 0)
qc.draw(output='mpl')

pm = PassManager([Unroller(['u1', 'cx']), Optimize1qGates()])
nqc = pm.run(qc)
nqc.draw(output='mpl')

This change is a part of the advocate project done under @nbronn.

[coveralls]

Pull Request Test Coverage Report for Build 1592690401

• 16 of 19 (84.21%) changed or added relevant lines in 1 file are covered.
• 5 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.002%) to 83.116%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
qiskit/transpiler/passes/optimization/optimize_1q_gates.py	16	19	84.21%

Files with Coverage Reduction	New Missed Lines	%
qiskit/extensions/quantum_initializer/uc.py	2	88.65%
qiskit/pulse/library/waveform.py	3	89.36%

Totals
Change from base Build 1587737912:	-0.002%
Covered Lines:	51914
Relevant Lines:	62460

---

💛 - Coveralls

[kdk]

Thanks for taking this on @rafal-pracht . This looks good so far, a few small comments below.

[rafal-pracht]

Thanks @kdk for your feedback, I've made changes.

[mtreinish]

This LGTM, thanks for the fast updates and sorry this has fallen through the cracks. The only thing missing here is a release note to document the new feature that the pass will work with unbound parameters on u1, u2, and p gates. You can see a guide on how to do this here: https://github.com/Qiskit/qiskit-terra/blob/main/CONTRIBUTING.md#release-notes once there's a release note here I think this is ready to merge

[mtreinish]

Closing this as the fork this PR was created from has been deleted so this PR is now effectively read only and we can't make modifications to the PR code anymore. This has been reopened from a new fork by the author at #7579 and we'll continue the review in that PR.