The Lexer now only provides the tokens to the parser, while the
parser is responsible for determining which attributes are placed
on notes. This only needs to be done when the attributes are
actually needed, rather than for all tokens.

This removes the usedAttributes lexer option (and lexer options
entirely). The attributes are now enabled unconditionally. They
have less overhead now, and the need to explicitly enable them for
some use cases (e.g. formatting-preserving printing) doesn't seem
like a good tradeoff anymore.

There are some additional changes to the Lexer interface that
should be done after this, and the docs / upgrading guide haven't
been adjusted yet.