track configs set from cli flags

[calebcartwright]

resolves #6252

There's more detail in that linked issue, but rustfmt internally needs to know whether the user explicitly specified a configuration value via a top level cli flag, e.g. --edition or --style-edition. This PR adds a separate boolean flag on configuration options that indicates whether the user specified it via a top level cli flag.

Notably, this intentionally does not make any changes to the config.set().* calls, nor the config.was_set().* behavior. That's because I'm unclear on the historical reasons why those ignored the CLI flag method, at this time I'm unclear on the potential side effects of changing that behavior, and we don't need to resolve nor risk any of that for the purposes of the 2024 work (i left an inline FIXME to revisit)

[calebcartwright]

As a thought for future cleanup on this, I think perhaps we can expand the programmatic config setting logic to take an argument indicating whether it's a user supplied value or a rustfmt internal override like one of these:

rustfmt/src/comment.rs

Line 760 in e21c1e2

config.set().wrap_comments(false);

And then the config setter logic can use that to determine whether or not to flip the flag