onnxruntime

Rework the native library usage so that a pre-built ORT native package can be easily used (#22345)

### Description
The local build of the native library was being included by almost every
project, but is only needed to run tests. Due to the multiple inclusions
attempting to use a pre-built package was clashing with any local builds
that were available.

Create a helper file to include either a local built of a pre-built
package and include that in the two test projects.

Cleanup various miscellaous things.

### Motivation and Context

Create setup to simplify running on-device tests with the nuget
packages.