[Layout foundations] Update `Columns` component docs and guidance

[laurkim]

Update Columns docs

• Description
• Examples: descriptions and visuals
• Add related components section

Update
Description	Displays content horizontally in one or more columns with equal spacing between.
Default example description	By default, there are 6 columns with 16px spacing between them.
Spacing example description	Use the spacing prop to set the amount of space between columns.
Column width example description	Individual column width can be adjusted.
Number of columns example description	Use the columns prop to set the number and width of columns across breakpoints.
Related components	For more control over padding and widths, use the Box component
	To lay out a set of smaller components horizontally, use the Inline component

Before and after

Link to Figma