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
* Refactor C# to handle x86
* update run script
* Add Native win x86 tests
* Add native x86 tests for Linux
* Update linux tests scripts to control which tests are run
* update linux image name for x86 to prevent using cached image
* update to not run unit python unit tests unless pybind is specified
* remove --build_wheel as a core common arg. Python cannot run on x86 build
* update OrtGetNumOfDimensions to OrtGetDimensionsCount in rest of C#