Allow type expansion of variants.

[gdotdesign]

This PR adds the feature / quality of life improvement of allowing variants to expand into their parent types in certain cases:

type User {
  age : Maybe(Number),
  name : String,
}

component Expansion {
  // Default properties
  property value : Maybe(String) = Just("Hello")
  
  // Initial state values
  state name : Maybe(String) = Nothing
  
  // Default argument values
  fun setName (name : Maybe(String) = Nothing)  {
    // Next calls
    next { name: Just("Joe") }
    next { name: name }
  }
  
  fun render {
    value or "FALLBACK"
  }
}

component Main {
  fun render {
	// Records and record updates
	{ age: Just(32), name: "Joe" }
	{ { age: Just(32), name: "Joe" } | age: Just(40) }
	
    // Html attribute values
    <Expansion value={Nothing}/>
  }
}

The main use case was to make Html less verbose, so this:

<Ui.View direction={Ui.Direction.Horizontal} flex={Ui.Flex.Fill}>
  <Ui.View
    flex={Ui.Flex.Custom("0 0 500px")}
    direction={Ui.Direction.Vertical}
    padding={4}
    gap={4}
  >
  ...
  </Ui.View>
</Ui.View>

can be written as:

<Ui.View direction={Horizontal} flex={Fill}>
  <Ui.View
    flex={Custom("0 0 500px")}
    direction={Vertical}
    padding={4}
    gap={4}
  >
  ...
  </Ui.View>
</Ui.View>

It's also useful in components where the states use ADTs and need to be written a lot.