Update `Config` to have a single field alignment option

[eureka-cpu]

This could look like:

pub struct Structures {
    /// Align fields of user defined structures to a threshold.
    pub field_alignment: FieldAlignment,
    /// Put small struct literals on a single line.
    pub struct_lit_single_line: bool,
}

pub enum FieldAlignment {
    AlignFields(usize),
    Off,
}

This would reduce the clutter in Config, remove the need for extra constants and take away the need for the user to input the same number for each type of alignment.

[kayagokalp]

Hmm, that looks good but in doing so wouldn't we block people from selecting which type to align (with different thresholds)? For example, would there be a case where a user wants to align enums and structs but not storage fields?

[eureka-cpu]

One thing mentioned before is that we don't want to make swayfmt "fully customizable" like rustfmt. I don't really see a user in the future that would want one aligned but not the other, but if those users do arise it's an easy fix. In the mean time it makes the use case much clearer and cleaner in the code itself.