Provide native support for U3 gate

[ACE07-Sev]

Adjust QasmUGate to have the same unitary as qiskit U3Gate.

Fixes #7634 and #5959

[ACE07-Sev]

To check correctness:

from cirq.circuits.qasm_output import QasmUGate
import cirq

from qiskit.circuit.library import U3Gate
from qiskit.quantum_info import Operator

import numpy as np

np.allclose(
    cirq.unitary(QasmUGate(0.1/np.pi, 0.2/np.pi, 0.3/np.pi)),
    Operator(U3Gate(0.1, 0.2, 0.3)).data
)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.38%. Comparing base (12b3906) to head (fa75343).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7717   +/-   ##
=======================================
  Coverage   99.38%   99.38%           
=======================================
  Files        1091     1091           
  Lines       97901    97907    +6     
=======================================
+ Hits        97295    97301    +6     
  Misses        606      606           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[pavoljuhas]

LGTM after adding tests and simplifying global phase evaluation.

Please let me know if it looks ok from your side.

[ACE07-Sev]

Should I add gamma as well to enable cu from qelib1.inc ? It's basically just missing a phase gate on the control index. We can add it as an additional parameter to QasmUGate and just add it to the global phase.
https://github.com/Qiskit/qiskit/blob/main/qiskit/qasm/libs/qelib1.inc#L130C1-L152

So instead of

phase_correction_half_turns = (self.phi + self.lmda) / 2

it would be

phase_correction_half_turns = (self.phi + self.lmda) / 2 + self.gamma

To minimize changes here we can make it have a default value of 0.