[js/web/training] runTrainStep implementation (#18006)
### Description
* based on design document & following InferenceSession's run
implementation, implemented TrainingSession.runTrainStep
### Motivation and Context
* Adding web bindings for training
#### Related work
* #16521 allowed for training artifacts to be built
* #17333 added interfaces for training
* #17474 allowed for training package to be built + added training
backend to web package
* #17891 implementation for createTrainingSession on the TypeScript side
**[SHOULD BE MERGED IN BEFORE THIS PR]**
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Co-authored-by: Yulong Wang <7679871+fs-eire@users.noreply.github.com>
Co-authored-by: Ashwini Khade <askhade@microsoft.com>
