TupleDescriptor performance improvements

[AlexUstinov]

This pull request mainly contains changes to speed up TupleDescriptor creation. It also reduces memory consumption by storing PackedFieldDescriptors in a compact structs instead of overflown with data fields classes.
There are other performance improvements (See commit messages).

The table below presents results of benchmarking of TupleDescriptor.Create method for tuples of length 1, 2, 3, 4 and 45.

|                  Method |               NuGetReferences |         Mean |      Error |     StdDev |  Gen 0 | Gen 1 | Gen 2 | Allocated |
|------------------------ |------------------------------ |-------------:|-----------:|-----------:|-------:|------:|------:|----------:|
| TupleDescriptor_Create1 |                         6.0.1 |     33.21 ns |   0.564 ns |   0.826 ns |      - |     - |     - |         - |
| TupleDescriptor_Create2 |                         6.0.1 |    512.05 ns |   3.245 ns |   4.654 ns | 0.1984 |     - |     - |     832 B |
| TupleDescriptor_Create3 |                         6.0.1 |    631.16 ns |   4.651 ns |   6.520 ns | 0.2251 |     - |     - |     944 B |
| TupleDescriptor_Create4 |                         6.0.1 |    771.58 ns |   5.467 ns |   7.484 ns | 0.2460 |     - |     - |    1032 B |
|  TupleDescriptor_Create |                         6.0.1 | 12,074.12 ns | 103.340 ns | 151.474 ns | 1.3580 |     - |     - |    5720 B |
| TupleDescriptor_Create1 | 6.0.3-tupledescriptor-nocache |     36.58 ns |   0.637 ns |   0.954 ns | 0.0210 |     - |     - |      88 B |
| TupleDescriptor_Create2 | 6.0.3-tupledescriptor-nocache |     62.41 ns |   0.899 ns |   1.317 ns | 0.0248 |     - |     - |     104 B |
| TupleDescriptor_Create3 | 6.0.3-tupledescriptor-nocache |    101.18 ns |   2.270 ns |   3.327 ns | 0.0286 |     - |     - |     120 B |
| TupleDescriptor_Create4 | 6.0.3-tupledescriptor-nocache |    131.02 ns |   2.397 ns |   3.514 ns | 0.0324 |     - |     - |     136 B |
|  TupleDescriptor_Create | 6.0.3-tupledescriptor-nocache |  1,378.13 ns |  14.367 ns |  21.505 ns | 0.1888 |     - |     - |     792 B |