[Testing] stackalloc arrays contain gcrefs

[hez2010]

Testing stackalloc arrays contain gcrefs.
We can allocate an array of pointers instead of flatting the whole content on the stack. Not sure about the gc report issue here.

The analysis is not correct currently, but I'm opening a PR to check the diff we can potentially have.

[hez2010]

@MihuBot

[hez2010]

@EgorBot -amd -arm -profiler

using System.Runtime.CompilerServices;
using BenchmarkDotNet.Attributes;
public class Benchmark
{
    [Benchmark]
    public void Bench()
    {
        var points = new[]
        {
            new Point(1, 2, 3),
            new Point(5, 4, 6),
            new Point(9, 8, 7),
        };
        double area = 0.5 * Math.Abs(
            points[0].X * (points[1].Y - points[2].Y) +
            points[1].X * (points[2].Y - points[0].Y) +
            points[2].X * (points[0].Y - points[1].Y));
        Use(area);
    }
    [MethodImpl(MethodImplOptions.NoInlining)]
    static void Use(double value) { }
    record Point(double X, double Y, double Z);
}

[hez2010]

This shares the same issue with field-wise analysis: we need to be careful with ind/blk load/store when field/index address is involved, which makes the analysis more conservative so that there will be fewer opportunities.
We need to make the analysis more precise.