cancel from Context API

[slinkydeveloper]

Expose the ability to do a one way call from the Context, then cancel/kill it from context too.

[nythrox]

Temporary workaround: if a workflows' own invocationId is exposed in the context (its already in ContextImpl, just needs to be made public) then workflows can expose a cancel handler which cancels itself using their invocationId and #412. External services can cancel it using the handler (ctx.workflowSendClient(Foo, key).cancel()).

I'm doing this for now by bypassing typescript's fake private fields and just grabbing ctx.stateMachine.invocation.debugId
With a bit of work you can make this work for services too, by making service calls self-register in some virtual object. Wouldn't recommend it.

[slinkydeveloper]

Train of PRs:

• Add CancelInvocation and GetCallInvocationId entries service-protocol#96
• Add CancelInvocation and GetCallInvocationId entries. #1967
• Implement GetInvocationId and CancelInvocation entries sdk-shared-core#10
• Get Invocation id/cancel invocation from Context sdk-rust#27
• Add tests for cancel invocation/get invocation id feature sdk-test-suite#11