Implement support for Highlight annotations

Fixes #5018.

Highlight annotations are basically nothing more than the already implemented Text annotations. Therefore a Highlight annotation can be represented as a Text annotation according to the PDF specification at https://www.adobe.com/content/dam/Adobe/en/devnet/acrobat/pdfs/pdf_reference_1-7.pdf#page=633&zoom=auto,-306,268. This change makes the annotations appear just like in Adobe Reader.

Note that for the issue above this PR fixes showing of the annotations, but the annotation content is rotated. This is a separate issue (due to the transform on the `annotText` that also affects child elements such as the annotation content) and I think it also related to #3826. This should be filed as a follow-up issue.