LibWeb: Convert numeric tokens to numbers in CSS Tokenizer

The spec wants us to produce numeric values as the Tokenizer sees them,
rather than waiting until the parse stage. This is a first step towards
that.

Userland/Libraries/LibWeb/CSS/Parser/Token.h

@@ -152,6 +152,7 @@ private:
     StringBuilder m_unit;
     HashType m_hash_type { HashType::Unrestricted };
     NumberType m_number_type { NumberType::Integer };
+    double m_number_value { 0 };
 
     Position m_start_position;
     Position m_end_position;