Originally the `xfaLayer` wasn't implemented in such a way that it supported being removed from the DOM when pages were evicted from the cache, however this limitation was lifted in PR 13427 and the `xfaLayer` should thus be handled similar to e.g. the `annotationLayer`.
In addition to removing the `xfaLayer` from the DOM, this patch *also* implements proper rendering/hiding-handling for it (mirroring the `annotationLayer`-code).
*Please note:* This patch is tagged API-minor just in case[1], since it changes the signatures of a couple of `PDFPageView`-methods to improve readability of the code.
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[1] Although users are *hopefully* not directly accessing any of the affected methods, and are rather using e.g. `PDFViewer` in which case none of these changes will matter.
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