chore: Update Core to a8150d5c (+job ordering update)

[mjameswh]

What was changed

• Update Core to a8150d5c.
• Updated Workflow Activation handling to expect InitializeWorkflow jobs, instead of StartWorkflow (fix [Feature Request] Update Core SDK: expect initializeWorkflow instead of startWorkflow jobs #1511).
• Delay payload conversion of workflow's memo/SA/lastfailure/etc until we're inside the sandbox, as there's no guarantee that converted payloads are safe to transfer through the V8 message port to the worker thread.

[Sushisource]

Makes sense to me!