Add first execution run ID for already-started start workflow results

[cretz]

Describe the solution you'd like

SDK needs StartWorkflowExecutionResponse.first_execution_run_id for on-conflict-use-existing situations, and WorkflowExecutionAlreadyStartedFailure.first_execution_run_id for other already-started situations. A lot of the time this will be populated with the same value as run_id.

Today, when SDK gets StartWorkflowExecutionResponse with started as false or WorkflowExecutionAlreadyStartedFailure, it doesn't include the first execution run ID that we can bind successive calls to. It only provides the run ID. If you start a workflow today successfully, SDK uses the run ID as the first execution run ID on successive calls like cancel and signal and such. But if you start a workflow today w/ conflict policy of use existing and it doesn't start, that run ID is not acceptable for first execution run ID.

[bergundy]

It's a bit involved but not too much of a heavy lift, there's some information that we don't have at the time when we handle the request that we would need to store in the current run persistence record.