Make WorkflowSavedStateRegistryAggregator.attachToParentRegistryOwner more convenient.

[rjrjr]

There are three copies of this fragment floating around:

    val parentRegistryOwner = stateRegistryOwnerFromViewTreeOrContext(this)
    val key = Compatible.keyFor(this.getRendering()!!)
    viewStateCache.attachToParentRegistryOwner(key, parentRegistryOwner)

Add an overload of WorkflowSavedStateRegistryAggregator.attachToParentRegistryOwner that takes a View and enshrines the convention.

Hide the existing method or leave it public? I have a hunch we may find ourselves calling it from Compose some day, if we start using its dialog() function.

[rjrjr]

Doubt we'll bother with this, and if we do introducing an overload is not a breaking change. Dropping from the ui-1.0 milestone.