bug#45780: 28.0.50; [PATCH] Face used for affixation function annotations

[Clemens]

> 1. when only annotation suffix string is provided, then the face
>     completion-annotations is added;
>
> 2. when both prefix and suffix are provided, then the client decides
>     what face to add.  Also it's possible to provide an empty prefix
>     string to be able to specify a custom face for the suffix string.
>
> So when the client wants to override the default annotation face,
> this is already easy to do using something like (this is not a patch
> to commit, but just demonstration of current abilities):

I would prefer the more automatic behaviour I proposed as having 
completion-annotations face is nice when the client has not thought 
about it but when the client has provided a string with a face it is 
likely the client wants exactly that face and not a combination with 
completion-annotations face. Basing the decision on a provided prefix 
seems a bit arbitrary and one would need to figure this out by looking 
at the code.