onnxruntime

Add iOS Swift Package Manager support (#15297)

### Description
<!-- Describe your changes. -->
Add Swift Package Manager (SPM) support for ORT based on  #14621
- uses the existing objective-c bindings
- some re-organization of the directory structure was required but the
contents of the files are unchanged, apart from adjustments due to file
movements

Add tool for updating ORT native pod used in the SPM package
Update CIs to use ORT native pod from build, and build/test using SPM



### Motivation and Context
<!-- - Why is this change required? What problem does it solve?
- If it fixes an open issue, please link to the issue here. -->
iOS developers are using SPM as much as cocoapods, so adding SPM means
both are catered for.