UpdateHandle should have a getResult method

[drewhoskins-temporal]

Is your feature request related to a problem? Please describe.

Usability nit. To get the result of the update, you have to do
handle.getResultAsync().get()
Given that updates are mostly used for synchronous use cases, could we make this more convenient?

Describe the solution you'd like
It makes sense to have a getResult() convenience helper that aliases the above code.

Describe alternatives you've considered

We considered renaming the async version to getResult() to be consistent with some other methods on the Java SDK.
But we decided that WorkflowStub has getResult/getResultAsync which is precedent enough given there's no way to be globally consistent.
And that having both is clearer and more usable.

Additional context
Add any other context or screenshots about the feature request here.