Generated GlideOptions are missing annotations

[TWiStErRob]

Glide Version: 4.5.0-SNAPSHOT

Integration libraries: none

Device/Android Version: none

Issue details / Repro steps / Use case background: Just looking around and noticed that com.bumptech.glide.request.RequestOptions#centerCrop has a warning on it saying "overriding methods are missing @NonNull". I checked where and it turns out it's from APT code. FlickrGlideExtension defines some of those methods, I wonder if it should warn/fail during processing that it's missing an annotation, or just add it automatically. Probably latter since all RequestOptions returning methods are builders and need to chain. On the other hand not having @NonNull in the extension class allows to return null without warning.

Glide load line / GlideModule (if any) / list Adapter code (if any):
https://github.com/bumptech/glide/blob/v4.4.0/samples/flickr/src/main/java/com/bumptech/glide/samples/flickr/FlickrGlideExtension.java

[TWiStErRob]

See also com.bumptech.glide.RequestManager#as

[sjudd]

Yeah and embarrassingly the centerCrop that's in that code is for testing and shouldn't have been committed :/.

[sjudd]

I'll add @nonnull by default to any methods generated from extensions and also warn if the extension itself is missing the annotation.