Add benchmark for ImmutableArrayExtensions

[prozolic]

Performance benchmark for ImmutableArrayExtensions.SequenceEqual method (related to dotnet/runtime#118932).
I have created a new ImmutableArrayExtensions class and added one benchmark. While there are other extension methods for ImmutableArrayExtensions, this implementation focuses only on ImmutableArrayExtensions.SequenceEqual.

[prozolic]

File name changed from ImmutableArrayExtensions.cs to Perf.ImmutableArrayExtensions.cs as well.

[DrewScoggins]

How long does a single operation end up taking? We just want to make sure that we are not in the low nanosecond range.

[prozolic]

The results themselves are the same as those listed in dotnet/runtime#118932.
The benchmark results are as follows:

| Method        | input       | Mean       | Error     | StdDev    | Median     | Min        | Max        | Gen0   | Allocated |
|-------------- |------------ |-----------:|----------:|----------:|-----------:|-----------:|-----------:|-------:|----------:|
| SequenceEqual | Array       |   5.671 ns | 0.3384 ns | 0.3897 ns |   5.544 ns |   5.419 ns |   7.055 ns |      - |         - |
| SequenceEqual | ICollection | 103.143 ns | 1.9016 ns | 1.7788 ns | 102.466 ns | 101.597 ns | 107.242 ns | 0.0037 |      32 B |
| SequenceEqual | IEnumerable | 107.665 ns | 2.1441 ns | 2.3832 ns | 106.737 ns | 105.110 ns | 113.926 ns | 0.0034 |      32 B |
| SequenceEqual | IList       |  53.489 ns | 0.1662 ns | 0.1555 ns |  53.459 ns |  53.242 ns |  53.848 ns |      - |         - |
| SequenceEqual | List        |   6.130 ns | 0.3136 ns | 0.3612 ns |   5.973 ns |   5.922 ns |   7.384 ns |      - |         - |

[xtqqczze]

@prozolic I don’t have enough familiarity with this repository to provide a proper review.

[DrewScoggins]

I will take a look at this today.

[xtqqczze]

I think it would sense to get this in before dotnet/runtime#118932 so we can properly validate the new implementation.