Implements an `ExpandedComponent`, which takes up as much space as
possible along the main axis within a `LinearLayoutComponent`. With more
than one `ExpandedComponent`, this expansion is divided equally.
`PaddingComponent` now inherits from `SingleLayoutComponent`.
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Co-authored-by: Lukas Klingsbo <lukas.klingsbo@gmail.com>
Co-authored-by: Lukas Klingsbo <me@lukas.fyi>