Fix ParameterExpression.is_real if symengine is installed

[Cryoris]

Summary

Fixes #8417.

Details and comments

This PR works around a case in symengine where an expression is not identified as real or imaginary if it is multiplied by a constant. This led to the unexpected behavior in Qiskit that e.g. 2 * I was not being identified as imaginary:

from qiskit.circuit import Parameter
x = Parameter("x")
expr = 1j * x
bound = expr.bind({x: 2})
print(bound.is_real())  # used to be True, but is now False

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[mtreinish]

LGTM, this seems reasonable to fix the bug while we wait for symengine. Hopefully they fix it soon and we can remove the extra eval call.

[coveralls]

Pull Request Test Coverage Report for Build 2799810266

• 5 of 5 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.004%) to 84.037%

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Totals
Change from base Build 2799807450:	0.004%
Covered Lines:	56089
Relevant Lines:	66743

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💛 - Coveralls