Improve S2589: Detect comparison between constant values

[gregory-paidis-sonarsource]

Comparing a constant value with another constant value does not make much sense.
The evaluation yields exclusively true or false, meaning the "conditional" code is always/never executed.

            const int constant1 = 42;
            const int constant2 = 42;
            const int constant3 = 43;

            if (constant1 == constant2) // Noncompliant, always true
            {
                DoWork(); // Always executed
            }

            if (constant1 == constant3) // Noncompliant, always false
            {
                DoWork(); // Never executed
            }

[pavel-mikula-sonarsource]

This should just start working out of the box when migrating to the new engine, as we already compute BoolConstraint from NumberConstraint comparisons.

[mary-georgiou-sonarsource]

Fixed by #7750