Entity{Ref,Mut}Except is duplicate functionality to FilteredEntity{Ref,Mut}

## Bevy version

0.15.2

## What you did

Working on animation stuff.

## What went wrong

`Entity{Ref,Mut}Except` are missing some functionality I need, like `get_by_id`. However, it appears that these types aren't used anywhere except the animation system, and it should be possible to replace them with the existing `FilteredEntity{Ref,Mut}`, which has all the functions I need.