masonry: add item layout with masonry modifier to skin

[megan-woodruff]

Description

Support masonry layout in Skin. As discussed with team previously, this will likely manifest as a CSS class for item layout with modifiers --grid and --masonry.

Some amount of JS is required to add the CSS styling to adjust the column heights, so there will be a linked Core UI ticket as well.

Screenshots

Figma link

https://www.figma.com/file/zEBdEhbonrBOGzZ0fXzWvM/eBay-Design-System?type=design&node-id=115062%3A162385&mode=dev

Engineering pre-requisites

• Successful design review with Design System Team.
• Supports dark mode.
• Supports responsive design.
• Tokens have been provided (or already exist).
• Successful accessibility review with Core A11Y Team.
• Successful frontend review with eBayUI Team.