### Description
<!-- Describe your changes. -->
Update some testing dependencies.
Fix various warnings. Mainly around documentation (existing) and unit
test usage (mainly resulting from xunit update).
Invalid angle brackets for generics in documentation were changed to use
curly braces based on
https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/xmldoc/
> To refer to generic identifiers in code reference (cref) elements, you
can use either the escape characters (for example, cref="List<T>")
or braces (cref="List{T}"). As a special case, the compiler parses the
braces as angle brackets to make the documentation comment less
cumbersome to the author when referring to generic identifiers.
### Motivation and Context
<!-- - Why is this change required? What problem does it solve?
- If it fixes an open issue, please link to the issue here. -->
### Description
1) Added Sequence And Maps convenience APIs to create input Sequences
and Maps
and also visit the outputs.
2) Address OrtValue design issue when the values are created on top of
the
managed memory and the ortValues are used for sequence and maps
creation.
We should retain the original managed instances that keep the memory
pinned.
We opt to keep track of those and dispose of them within an instance of
OrtValue
that represents a Map or a Sequence.
3) Set `LangVersion` to default per [MS Versioning
Docs.](https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/configure-language-version)
### Motivation and Context
1) When writing code examples, use of Map and Sequences API proved to be
cumbersome.
2) It is a BUG, that we should address, as the managed memory can move
by the GC and lead to
intermittent crashes.
3) Make use of the most feature of the C#.
### Description
Expose `OrtValue` class API as first-class citizen.
Make it simular with C++ API.
Enable safe direct native memory access.
Make string tensor manipulation more efficient.
Avoid intermediate structures such as `NamedOnnxValue`,
`DisposableNamedOnnxvalue` and etc.
Provide more examples with `IOBinding`, although `OrtValue` API
potentially makes `IOBinding` redundant for most of scenarios, since
`OrtValue` can be created on top of any memory.
Run all the pre-trained models now with `OrtValue` API as well.
Obsolete `OrtExternalMemory class`. Obsolete IOBinding API that takes
`FixedBufferOnnxValue`.
### Motivation and Context
Make the API efficient and uniform with C++.
This aspires to address:
https://github.com/microsoft/onnxruntime/issues/14918https://github.com/microsoft/onnxruntime/issues/15381
Cc: @Craigacp
### 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.
