Scoped constructor parameters should be able to reference top-level locals

[RikkiGibson]

class C2
{
    public C2(scoped Span<int> span)
    {
        int x = 0;
        span = new Span<int>(ref x); // error
    }

    void M(scoped Span<int> span)
    {
        int x = 0;
        span = new Span<int>(ref x); // ok
    }
}

Expected: both span assignments are ok
Actual: It is an error in constructor but ok in ordinary method.

This is happening because of public override BoundNode? VisitConstructorMethodBody() in RefSafetyAnalysis.cs. Creating the LocalScope in that situation (which is necessary to hold any temps etc created for visiting the constructor initializer), is causing us to increment the local scope depth an extra time, treating the top-level locals as if they have a smaller lifetime than the scoped parameters.