Provide last result and last failure to workflows

Describe the solution you'd like

Go, Java, and TypeScript all provide a way to get the "last result" and "last failure" if this was via cron or schedule (come over in workflow start history as last_completion_result and continued_failure). Newer SDKs should too.

Even though this is immutable data and was put on TypeScript as info, Go and Java have this directly on the workflow context and it'll make sense for newer SDKs to do the same. Also make sure there is an obvious way to differentiate the absence of a "last result" and a null one.

Also, although it's technically an array in history/Core, langs should treat this as a single value.

Per-SDK Tickets

• Go - Done
• Java - Done
• Core - Done
• TypeScript - Done
• Python - https://github.com/temporalio/sdk-python/issues/383
• .NET - https://github.com/temporalio/sdk-dotnet/issues/489
• Ruby - https://github.com/temporalio/sdk-ruby/issues/281
• PHP - Done (maybe missing last error?)
• Temporal CLI - N/A

Start with the Ruby ticket linked in the per-SDK checklist, then compare the completed Go, Java, and TypeScript implementations referenced here. Confirm how the workflow context exposes last_completion_result and continued_failure, including the distinction between an absent value and null, and ensure the history array is represented as one value.