8794: Give MergeBehaviour variants better names r=Veykril a=Veykril
I never really liked the variant names I gave this enum from the beginning and then I found out about rustfmt's `imports_granularity` config:
> imports_granularity
>
> How imports should be grouped into use statements. Imports will be merged or split to the configured level of granularity.
>
> Default value: Preserve
> Possible values: Preserve, Crate, Module, Item
> Stable: No
I personally prefer using `crate` over `full` and `module` over last, they seem more descriptive. Keeping these similar between tooling also seems like a good plus point to me.
We might even wanna take over the entire enum at some point if we have a `format/cleanup imports` assists in the future which would probably want to also have the `preserve` and `item` options.
Co-authored-by: Lukas Wirth <lukastw97@gmail.com>