Update screens types

[bradlc]

This PR updates the theme.screens and theme.container.screens types, ensuring that it supports the following formats for individual screens:

string
{ raw: string }
{ min: string }
{ max: string }
{ min: string, max: string }
Array<{raw: string} | { min: string } | { max: string } | { min: string, max: string }>

It also handles an array of strings at the top level, e.g.

module.exports = {
  theme: {
    screens: ['100px', '200px'],
  },
}

Before:

After: