To make this functionality work out-of-the-box in custom implementations, see e.g. the "viewer components" examples, it'd be slightly easier if we dynamically create/insert the "hiddenCopyElement" in the `PDFViewer` constructor.
Given that the "copy all text" feature still appears to work just as before with this patch, hopefully I'm not overlooking any reason why doing this would be a bad idea.
The tag <base> is used to resolve relative URIs within the document.
Newly added SVG filters use a relative URI which then use the URI in base
but this one mismatches with the document URI and consequently filters are
not found in the Firefox viewer.
So this patch just removes <base> and replace few relative URLs by absolute
ones.
This further extends the web-specific import maps introduced in PR 16009, to allow removing *most* of the build-time `require` statements from the viewer. The few remaining ones are fallbacks used for the COMPONENTS respectively the `legacy` GENERIC builds.
Given that the GV-viewer isn't using most of the UI-related components of the default-viewer, we can avoid including them in the *built* viewer to save space.[1]
The least "invasive" way of implementing this, at least that I could come up with, is to leverage import maps with suitable stubs for the GV-viewer.
The one slightly annoying thing is that we now have larger import maps across multiple html-files, and you'll need to remember to update all of them when making future changes.
---
[1] With this patch, the built `viewer.js` size is 391 kB and `viewer-geckoview.js` is 285 kB.
