Normalize items before uniqueness calculation

[bartveneman]

For The CSS Selection it makes a ton of sense to only know about normalized data. Some examples:

• For property browserhacks we currently story *zoom and *display as unique values. The hack they use is the same, so they could be stored as 2 usages of the * hack
• For color analysis we store red and RED as two separate values. They could be one.
• For color format analysis we already normalize: everything is marked as hex3, rgb etc.
• Accessibility selectors could be grouped by aria-*=value and role=value instead of storing each unique selector as a unique entry

And this list goes on and on.