EngineObjectData changes

This PR has two changes (each in its own commit):

The first adds the interface `EngineObjectData.Sync`, a subtype of `EngineObjectData` that includes synchronous getters and setters.  It also updates `ResolvedEngineObjectData` (and a few other impls of EOD) to use this new interface.  Finally, the default data fetcher in `ViaductWiringFactory` is modified to look for an use this interface -- rather than look for `ResolvedEngineObjectData` and extract its `data` property -- when it optimizes for the synchronous case.  This is a more encapsulated way to support synchrnous EODs.

The second changes adds the function `EngineObjectData.fetchSelections`, which returns an `Iterable<String>` of the selections available on the current object.  The intended use of this function is to build bindings into languages that do not support Kotlin's suspending functions: before calling into such languages, in Kotlin we can use this method to (recursively) convert and EOD into something easier for another language to process (eg, a `Map<String, Any?>`).
Github-Change-Id: 945946
GitOrigin-RevId: 2bc03dc40a10017e47a39994e08748728aedbf4a

Release 0.3.0

Publish Viaduct API docs with Dokka

Github-Change-Id: 932650
GitOrigin-RevId: 639c60dee63d873a25546bad8d1ec47e632ee978