Reduce allocations and speed up AsScalar
Reduce allocations and speed up AsScalar

BenchmarkDotNet=v0.12.1, OS=Windows 10.0.17763.1397 (1809/October2018Update/Redstone5)
Intel Xeon Silver 4114 CPU 2.20GHz, 2 CPU, 20 logical and 20 physical cores
.NET Core SDK=5.0.200-preview.21077.7
  [Host]     : .NET Core 3.1.10 (CoreCLR 4.700.20.51601, CoreFX 4.700.20.51901), X64 RyuJIT
  DefaultJob : .NET Core 3.1.10 (CoreCLR 4.700.20.51601, CoreFX 4.700.20.51901), X64 RyuJIT

|      Method |   test |        Mean |     Error |    StdDev |  Gen 0 | Gen 1 | Gen 2 | Allocated |
|------------ |------- |------------:|----------:|----------:|-------:|------:|------:|----------:|
|    AsScalar |  Empty |  56.1461 ns | 0.4543 ns | 0.3794 ns | 0.0077 |     - |     - |      56 B |
| AsScalarNew |  Empty |   3.5915 ns | 0.0066 ns | 0.0062 ns |      - |     - |     - |         - |
|    AsScalar | Scalar | 143.9243 ns | 0.5904 ns | 0.5234 ns | 0.0134 |     - |     - |      96 B |
| AsScalarNew | Scalar | 109.7074 ns | 0.4356 ns | 0.3861 ns | 0.0077 |     - |     - |      56 B |
|    AsScalar |   null |   1.4991 ns | 0.0085 ns | 0.0080 ns |      - |     - |     - |         - |
| AsScalarNew |   null |   0.4151 ns | 0.0081 ns | 0.0075 ns |      - |     - |     - |         - |

object/Simple.OData.Client,object/Simple.OData.Client