Merge paramterized u1, u2 and p gate in Optimize1qGates

[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.

This is continuation of the issue #7309

[mtreinish]

I'm a bit confused by this PR, it looks identical to #7309 except you've added the release note I asked for in my review yesterday. To add the release note there is no need to open a new pull request you can just modify the existing branch for #7309. It's generally better to use the existing PR so the entire review history is present and the merged commit refers to the single place where all the review happened.

[rafal-pracht]

@mtreinish you are absolutely right. I'm unable to add release notes to PR because I'm also working on the @nbronn fork of terra and GitHub lost the connection between my code and the last PR. Therefore I've created a new one with exactly the same code with the release notes added.

Sorry for confusion.

[coveralls]

Pull Request Test Coverage Report for Build 1762015271

• 16 of 19 (84.21%) changed or added relevant lines in 1 file are covered.
• 3 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.001%) to 83.149%

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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/pulse/library/waveform.py	3	89.36%

Totals
Change from base Build 1761987769:	0.001%
Covered Lines:	51905
Relevant Lines:	62424

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💛 - Coveralls

[mtreinish]

It looks like some of the revisions made on #7309 didn't make it through the transition to this new PR. I also left some inline improvement suggestions on the release note. Mostly around som sphinx rst syntax fixes and some mild rewording.

[rafal-pracht]

@mtreinish I've added those changes.

[mtreinish]

LGTM, thanks for keeping with this and making the updates