The bug was supposed to be fixed by #20471 but here there are some annotations in the pdf.
When those annotations are added to the DOM, the struct tree has to be rendered but without
the text layer (because of asynchronicity).
So this patch is making sure that the modifications in the text layer are done once the
layer is rendered.
This way, the screen readers can read the math content properly.
The elements in the text layer will also have aria-hidden="true"
to avoid duplication.
It'll help to make math equations "visible" for screen readers.
MS Office has a specific way to add some MathML code to struc tree leaf
and this patch handles it.
To avoid being able to introduce dependencies between tests this commit
makes sure that we close the document between tests so that we can't
accidentally rely on state set by a previous test.
The idea is to insert a span in the text layer with an aria-role set to img
and use the bounding box provided by the attribute field in the tag dict in
order to have non-null dimensions for the image to make it "visible".
