Add Native AOT test projects for M.E.AI

[stephentoub]

Work has been done to make the M.E.AI libraries safe for use in Native AOT applications, but we need a) a test project that roots everything and builds error free, and b) a test suite that runs a reasonable subset of tests in a Native AOT app.

cc: @eiriktsarpalis, @SteveSandersonMS

[stephentoub]

#5573 implemented (a), but it needs to be hooked up to CI to actually dotnet publish.

[stephentoub]

The test project is now being published in CI.

Work remaining is to actually run some tests under Native AOT.