Send signal to workflow via parent interface

[smelesh]

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What was changed

Add an ability to create workflow stub without a handler method, so that signals can be sent to a running workflow via parent reusable interface.

Why?

Workflow interface inheritance is broken because workflow stub can not be created without a handler method annotated with WorkflowMethod.

Handler method is needed only to start a new workflow, but it's okay to send signals or queries to other workflows by stub created from a reusable parent interface.

Checklist

1. How was this tested:

Integration tests

[CLAassistant]

All committers have signed the CLA.

[rustatian]

Friendly ping @wolfy-j / @roxblnfk