Page Builder Elements

[adrians5j]

Changes

This PR introduces a new @webiny/app-page-builder-elements package, which provides an easier system for dealing with rendering page elements. The following are some of its features:

• no plugins, developers just mount the PageElementsProvider, to which they pass page element renderers, modifier functions that deal with page elements' properties (e.g. width, height, shadow, other custom properties), theme, and so on
• everything is managed using Emotion CSS-in-JS solution, no SCSS is needed
• only a single dependency (Emotion), potentially we could also allow a custom CSS-in-JS solution one day
• using built-in hooks, developers can easily apply the built-in styles to their custom elements (styles that were set through the PB Editor like padding, margin, background color, ...)
• a central theme object is also passed to the provider, enabling developers to define breakpoints and styles for any component that they might have
• CSS can be written for multiple breakpoints

How Has This Been Tested?

Manual testing.

Documentation

For now, this is a preview / PoC level implementation, so no documentation yet.