JIT: Treat store in JTRUE block as the ElseOperation in if-conversion

[BoyBaykiller]

If-conversion phase now produces the same IR for these two cases:

bool First(int tMinLeft, int tMinRight)
{
    bool leftCloser = false;
    if (tMinLeft < tMinRight)
    {
        leftCloser = true;
    }
    return leftCloser;
}

bool Second(int tMinLeft, int tMinRight)
{
    bool leftCloser;
    if (tMinLeft < tMinRight)
    {
        leftCloser = true;
    }
    else
    {
        leftCloser = false;
    }
    return leftCloser;
}

The last unconditional store (leftCloser = false) is substituted into the SELECT which enables further optimization. Specifically it fixes #124713.

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[BoyBaykiller]

@dotnet-policy-service agree

[BoyBaykiller]

@a74nh @jakobbotsch PTAL

[BoyBaykiller]

This logic could for sure be made smarter to catch more cases but it's the best I can do for now. If we ever get a HIR version of IsInvariantInRange then we could use it here.