C#: Increase precision of cs/constant-condition.

[michaelnebel]

In this PR we start to take conditions into account for matching in switch statements and expressions. That is, we allow match all (discard) patterns, if there is a condition. Furthermore, we also apply the logic to switch/case statements.

Example

public string M(int i)
{
    return i switch
    {
        _ when i % 2 == 0 => "even", // We used to flag this in cs/constant-condition
        _ => "odd"
    };
}

This reduces the number of false positives.

DCA looks good.

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[hvitved]

A small stylistic suggestion, otherwise LGTM.