[experiment feedback] gs commit pick #905

This issue tracks the work to stabilize the 'gs commit pick' experimental command introduced in #536.
Feel free to post feedback here if you use the experimental command.

Known issues (not all of these will be resolved before stabilization):

• Handling of conflicting changes: If cherry-picked changes cannot be applied without a conflict, we currently reject the operation. We should provide users the ability to resolve the conflict instead.
• Hooks: The operation does not invoke any Git hooks.