Support for other markup types with pdf-annot

[sati-bodhi]

In pdf-annot-markup-annotation-types, we see a long list of "defined markup annotation types".

(text link free-text line square circle polygon poly-line highlight underline squiggly strike-out stamp caret ink file sound)

But only a few are "listed" and supported in pdf-annot-list-listed-types:

(text file squiggly highlight underline strike-out)

Just wondering if it is possible to extend the supported type at least to lines, squares and circles so that markup can be done more freely, especially when ocr (which most of the support types rely on) is not done or done poorly.

(add-to-list 'pdf-annot-list-listed-types 'square)

doesn't change anything, functionally speaking.