In this change I went through all current rustfmt configuration options
and expanded our existing configuration with overrides whenever deemed
appropriate.
The `normalize_doc_attributes` option is still unstable, but seems to
work without any issues. Even when passing macros like `include_str!`
that is recognized properly and not normalized. So while this wasn't an
issue anywhere in the code, it should make sure it never will be.
When it comes to imports there are two new major additions. The
`imports_granularity` and `group_imports` options. Both mostly just
incorporate unwritten rules that have existed in Alacritty for a long
time. Unfortunately since `alacritty_terminal` imports in `alacritty`
are supposed to be separate blocks, the `group_imports` option cannot be
used.
