This uses the new `spacing` feature of the `Layout` struct to allocate
columns spacing in the `Table` widget.
This changes the behavior of the table column layout in the following
ways:
1. Selection width is always allocated.
- if a user does not want a selection width ever they should use
`HighlightSpacing::Never`
2. Column spacing is prioritized over other constraints
- if a user does not want column spacing, they should use
`Table::new(...).column_spacing(0)`
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Co-authored-by: Josh McKinney <joshka@users.noreply.github.com>
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