feat: add TOML formatter

Ports taplo 0.14.0: its lexer, its parser, which builds the same
tree as rowan, and its formatter. The lexer follows logos 0.12,
quirks included: when it backtracks out of a date, a time or an
exponent, the token is an INTEGER. It matches logos on 10M random
texts, and taplo on 22,158 of 22,167 runs over local repos; the
rest is a file with a byte order mark, which taplo rejects.