onnxruntime

Objective-C Add Support to Create and Query String ORTValues (#16764)

This pull request contains a few changes:

1. Adds support for string ort values.
2. Fixes the training minimal build (that was broken with #16601) by
putting custom op registration behind #ifdefs
3. Fixes the iOS pod package generation (that was again broken with
#16601) by explicitly providing paths to be copied during pod creation.