Add WinML Model testing (#5417)
* Model test start with float
* Clean up code and add environment variable detection
* Move into namespace
* PR comments
* Fix linker errors in latest merge to master and also fix warning
* add skipping model test mechanism
* Return std::string instead of writing to buffer
* Address case where env variable is larger than max_path
* use const static string for test reason
* Disable x86 tests and don't build if ort memory checker is enabled
* Add comment
* Add additional failing x86 tests and ifdef for checking fo rx86 build
* PR comments
