Closes#3472
What this does:
- Removes use of `Config` options that were partially implemented
- Fixes the default implementations for `Config`. This removes the match
arms in the implementations of the `CurlyBrace` trait and just handles
the default, eg `ItemBraceStyle::SameLineWhere`
- Adds tests for items with `where` clauses, ie `ItemImpl`,
`ItemStruct`, `ItemTrait`, which weren't being tested thoroughly enough
- Updates to code quality in the `Config`, and documentation for the
default config's options
## Description
- closes#3296
- closes#3297
## Checklist
- [x] I have linked to any relevant issues.
- [x] I have commented my code, particularly in hard-to-understand
areas.
- [x] I have updated the documentation where relevant (API docs, the
reference, and the Sway book).
- [x] I have added tests that prove my fix is effective or that my
feature works.
- [x] I have added (or requested a maintainer to add) the necessary
`Breaking*` or `New Feature` labels where relevant.
- [x] I have done my best to ensure that my PR adheres to [the Fuel Labs
Code Review
Standards](https://github.com/FuelLabs/rfcs/blob/master/text/code-standards/external-contributors.md).
- [x] I have requested a review from the relevant team or maintainers.
