Missing methods for returning excess in Alloc

Returning `Excess` when allocating is useful for collections like (`Raw`)`Vec`. Currently, only these methods are provided:

- `alloc_excess`
- `realloc_excess`

In order to make those collection work with the excess api, these methods have to be added:
- `alloc_zeroed_excess`
- `grow_in_place_excess`
- `shrink_in_place_excess`