Ensure nested selectors using &:hover work

[RobinMalfait]

This PR will fix an issue where nested configuration in the tailwind.config.js didn't get the correct selector.

E.g.:

theme: {
  extend: {
    typography: {
      DEFAULT: {
        css: {
          a: {
            color: '#888',
            '&:hover': {
              color: '#ff0000',
            },
          },
        },
      },
    },
  },
},

This generated the incorrect css:

.prose a {
  color: #888;
  text-decoration: underline;
  font-weight: 500;
}

:where(.prose a:hover):not(:where([class~="not-prose"] *)) {
  color: #FF0000;
}

This means that the non-hover version still has higher specificity. The output we want is this:

.prose :where(a):not(:where([class~='not-prose'] *)) {
  color: #888;
  text-decoration: underline;
  font-weight: 500;
}

.prose :where(a):not(:where([class~='not-prose'] *)):hover {
  color: #ff0000;
}

Fixes: #231

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[jacobdalamb]

This breaks dark mode css customization with prose class.