Fix bugs related to view controller containment

[n8chur]

Overview

• Adds additional view controller property forwarding to contained view controllers in ContainerViewController and DescribedViewController
• Fixes a missing preferred content size update and avoids updating the preferred content size in a few cases where it did not previously
• Adds contained child view controllers as children in the initializer for these containers. This allows consumers to inspect properties of the view controller before the view has loaded and get appropriate values—previously this would return a default value until the view was loaded even though the information was available.

Checklist

• Unit Tests
• UI Tests
• Snapshot Tests (iOS only)
• I have made corresponding changes to the documentation

[CLAassistant]

All committers have signed the CLA.

[n8chur]

• Move view controller containment (addChild etc.) to initializers

[n8chur]

This containment / preferredContentSize pattern has been used in Market and has proven to work well for us so far!