This patch doesn't structurally change the text layer: it just adds some aria-owns
attributes to some spans.
The aria-owns attribute expect to have an element id, hence it's why it adds back an
id on the element rendering an annotation, but this id is built in using crypto.randomUUID
to avoid any potential issues with the hash in the url.
The elements in the annotation layer are moved into the DOM in order to have them in the
same "order" as they visually are.
The overall goal is to help screen readers to present to the user the annotations as
they visually are and as they come in the text flow.
It is clearly not perfect, but it should improve readability for some people with visual
disabilities.
Given that none of these CSS rules are used at all, unless debugging is enabled, it seems completely unnecessary to load them *unconditionally* for all users.[1]
Note that if *both* the `textLayer` and `pdfBug` debugging hash-parameters are specified simultaneously, we'll now load the `PDFBug`-file *twice* (since the code is simpler that way). However, given first of all that none of this is enabled by default and secondly that using those parameters together isn't helpful[2], potentially loading that file twice is hopefully not an issue.
For the `gulp mozcentral` target, the size of the *built* `viewer.css` file is reduced `> 3%` with this patch.
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[1] For the Firefox built-in PDF Viewer, in order to even be able to access the `PDFBug` functionality, you need to first of all set `pdfjs.pdfBugEnabled = true` manually in `about:config`. Secondly, you then also need to append the `pdfBug=...` hash-parameter to the URL when *initially* loading the document.
[2] Note how the `textLayer`-settings are already, since essentially forever, overriding the highlighting-features of the "FontInspector"-tab.
