Polish matchVariant API

[RobinMalfait]

This PR will polish the currently unreleased matchVariant API. This API will allow you to create
dynamic variants. E.g.: supports-[display:grid]:grid.

The API looks very similar to the addVariant API, but with a callback instead.

An example for demonstrating the API:

matchVariant('supports', ({ value }) => `@supports(${value})`, {
  values: {
    grid: 'display: grid', // Allows us to use just `supports-grid`
  },
})

Input:

<div class="supports-grid:grid supports-[color:red]:text-red-500"></div> 

Output:

@supports (display: grid) {
  .supports-grid\:grid {
    display: grid;
  }
}

@supports (color: red) {
  .supports-\[color\:red\]\:text-red-500 {
    --tw-text-opacity: 1;
    color: rgb(239 68 68 / var(--tw-text-opacity));
  }
}

Note: the API is still subject to change, this is currently a placeholder.