This PR is similar to and a follow up of #18815, but this time to
migrate the `data` theme keys.
Let's imagine you have the following Tailwind CSS v3 configuration:
```ts
export default {
content: ['./src/**/*.html'],
theme: {
extend: {
data: {
// Automatically handled by bare values
foo: 'foo',
// ^^^ ^^^ ← same names
// Not automatically handled by bare values
bar: 'baz',
// ^^^ ^^^ ← different names
// Completely custom
checked: 'ui~="checked"',
},
},
},
}
```
Then we would generate the following Tailwind CSS v4 CSS:
```css
@custom-variant data-bar (&[data-baz]);
@custom-variant data-checked (&[data-ui~="checked"]);
```
Notice how we didn't generate a custom variant for `data-foo` because
those are automatically handled by bare values.
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