### Description
Enable support for building iOS packages/CocoaPods with training API
- Add `Training` Package variant and config files in current iOS
packaging utilities to enable creation of training packages
### Motivation and Context
This PR introduces new `Training` variant in
`build_and_assemble_ios_pods.py` script which allows creating pods for
iOS with training API enabled.
The sample script to build training pods:
```
python3 tools/ci_build/github/apple/build_and_assemble_ios_pods.py --variant Training \
--build-settings-file tools/ci_build/github/apple/default_full_ios_training_framework_build_settings.json \
-b=-- path_to_protoc_exe=<path/to/protoc>
```
Note: build settings file should have `--enable_training` as a build
parameter.
Simply adding training packaging increases the duration of the Azure
pipeline for packaging by 70 minutes. To address this issue, we need to
parallelize pod creation. In order not to further strain the pipeline,
the changes for training packaging will be added in another PR, which
optimizes the packaging pipeline.
---------
Co-authored-by: Edward Chen <18449977+edgchen1@users.noreply.github.com>
### Description
Implement Objective-C binding for `ORTCheckPoint`. Additionally,
- Modify `onnxruntime_objectivec.cmake` to only include training header
and sources when training flag is enabled
- Enable objective-c binding for `orttraining-mac-ci-pipeline`
### Motivation and Context
This PR is part of implementing Objective-C bindings for training API.
It implements objective-c binding for ORTCheckPoint class. The
objective-C API closely resembles the C++ API.
**Note**: The test for saving checkpoint is skipped as it requires use
of training session. It will be added when the objective-c binding for
`ORTTrainingSession` is added.
