Refactoring: shared utilities and cleanup

[dandavison]

This is pure refactoring aimed at slightly reducing friction when adding new features:

• New harness utilities for starting a workflow with default options: start_parameterless_workflow and executeParameterlessWorkflow for Python and Typescript respectively.

• Convert child_workflow/result Java feature to use single feature.java file (and move ChildWorkflow impls inside ChildWorkflow interface)

• Make use of runner.executeSingleParameterlessWorkflow in a Java feature that wasn't using it.

[dandavison]

The diff here is mostly indentation, moving an impl into the interface - easier to understand with hide-whitespace on.

[dandavison]

The diff in the file is easier to understand with hide-whitespace on: spotless converting 4-space to 2-space indentation.

[cretz]

Greatly appreciated! I think on the Java SDK there is an auto-formatter. I wonder if we want to bring that over here.

[dandavison]

You do have the "spotless" autoformatter active here, which is what made these changes. I guess it tolerates both 4- and 2-space indentation depending on context and I caused it to flip. But I thought I'd let it do its thing because it seems we mostly use 2 spaces.

[dandavison]

Now that we're adding more multiple-workflow features, I briefly looked into changing the Java harness so that we can define multiple workflows symmetrically (rather than having one standalone workflow interface and the other workflow interface implemented by the feature), but it's fairly deeply engrained in the harness design:

features/harness/java/io/temporal/sdkfeatures/PreparedFeature.java

Line 57 in 0ec38b2

this.metadata = POJOWorkflowImplMetadata.newInstance(factoryClass);

so I left that.

[cretz]

Greatly appreciated! I think on the Java SDK there is an auto-formatter. I wonder if we want to bring that over here.

[dandavison]

Thanks for reviewing @cretz!