AS is always required in Widget annotations

[bdoubrov]

AnnotWidget.tsv currently specifies that the AS entry is required if fn:IsRequired(fn:IsPresent(AP::N::*) || fn:IsPresent(AP::R::*) || fn:IsPresent(AP::D::*)).

This corresponds to the following phrase from PDF spec: AS is "Required if the appearance dictionary AP contains one or more subdictionaries". However, for example, the condition fn:IsPresent(AP::N::*) evaluates to true for AP entry having value of type dictionary or stream. So, as a result, AS entry is always required, which is not correct.

And I don't immediately see how to fix this within the current grammar.