### Description
<!-- Describe your changes. -->
MAUI test app with tooling to add model and generated or provided input
test data.
The app will load the model and validate the output. It can also run a
specified number of iterations to provide basic performance information.
<img width="401" alt="image"
src="https://github.com/microsoft/onnxruntime/assets/979079/daf3af13-fb22-4cbb-9159-486b483a7485">
### 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. -->
Primarily to make it easier to test an arbitrary model on iOS. A MAUI
app allows testing on all platforms.
---------
Co-authored-by: Edward Chen <18449977+edgchen1@users.noreply.github.com>
Add Xamarin support to the ORT nuget packages.
- Update C# code to support Xamarin builds for iOS and Android
- refactor some things to split out common code
- include iOS and Android ORT native shared library in native nuget package
