Avoid OrderBy.ToArray/ToList overheads for length 1

[stephentoub]

We already special-case length 0. That can trivially be extended to length 1.

using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;

BenchmarkSwitcher.FromAssembly(typeof(Tests).Assembly).Run(args);

[MemoryDiagnoser(false)]
[HideColumns("Job", "Error", "StdDev", "Median", "RatioSD")]
public class Tests
{
    private IEnumerable<string> _data;

    [Params(1)]
    public int Count { get; set; }

    [GlobalSetup]
    public void Setup() => _data = Enumerable.Range(0, Count).Select(i => i.ToString());

    [Benchmark]
    public string[] OrderArray() => _data.Order().ToArray();

    [Benchmark]
    public List<string> OrderList() => _data.Order().ToList();
}

Method	Toolchain	Count	Mean	Ratio	Allocated	Alloc Ratio
OrderArray	\main\corerun.exe	1	85.30 ns	1.00	336 B	1.00
OrderArray	\pr\corerun.exe	1	33.53 ns	0.39	120 B	0.36
OrderList	\main\corerun.exe	1	91.46 ns	1.00	392 B	1.00
OrderList	\pr\corerun.exe	1	42.60 ns	0.47	184 B	0.47

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