onnxruntime

Implement Optional Metadata support and C# test support (#15314)

### Description
Implement Optional Type metadata support in the library.
Implement optional support in C# API along with metadata.
Implement Sequence, Map, Optional test data support
and test execution.

Prune tests and provide more details for failing tests in C# code.

Note, this PR does not enable running onnx test models in C++.

### Motivation and Context
Opset18 optional type support.