onnxruntime

Adust GetVersionString() GetBuildInfoString() signatures and move them to OrtApi (#15921)

### Description

This PR partially reverts changes introduced in
https://github.com/microsoft/onnxruntime/pull/15643

We make two API return std::string always in UTF-8.

We also move the entry points from OrtApiBase to OrtApi to make them
versioned.

### Motivation and Context

`GetVersionString` always returns x.y.z numbers that are not subject to
internationalization.
`GetBuildInfoString` can hold international chars, but UTF-8 should be
fine to contain those.
We prefix them with u8"" in case the compiler default charset is not
UTF-8.
Furthermore, creating platform dependent APIs is discouraged.
`ORTCHAR_T` is platform dependent and was created for paths only.
On non-unix platforms would still produce `std::string` that can only
contain UTF-8

The API was introduced after the latest release, and can still be
adjusted.