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

[laurkim]

Update Bleed docs on polaris.shopify.com

• Description
• Examples: descriptions and visuals
• Add bleed values section

Update
Description	Applies negative margin to allow content to bleed out into the surrounding layout.
Vertical example	Content will bleed vertically into the surrounding layout using the vertical prop.
Horizontal example	Content will bleed horizontally into the surrounding layout using the horizontal prop.
Specific direction example	Content will bleed into the surrounding layout in a specific direction using the top, bottom, left, or right prop.
All directions example	Content will bleed into the surrounding layout in all directions using the spacing prop.
Add section "Bleed values"	Content should never go beyond the edges of the parent container. Choose a bleed value that works within the containing layout.

Before and after

Link to Figma