Run function/forwardRef components in component zone, run children tests

[greglittlefield-wf]

Motivation

• Render logic for function and forwardRef components weren't being run in the component zone, which was inconsistent with class-based components.
• Existing children tests that verify children are always Lists in Dart weren't being run for function and forwardRef components

Solution

• Add component zone logic and tests to commonFactoryTests
• Run commonFactoryTests for forwardRef components
• Update children tests to run for function and forwardRef components

Testing

• Tests pass
• Revert changes in https://github.com/cleandart/react-dart/pull/269 and verify that children tests fail