[api-minor] Implement basic support for OptionalContent Usage dicts (issue 5764, bug 1826783)

The following are some highlights of this patch:
 - In the Worker we only extract a *subset* of the potential contents of the `Usage` dictionary, to avoid having to implement/test a bunch of code that'd be completely unused in the viewer.

 - In order to still allow the user to *manually* override the default visible layers in the viewer, the viewable/printable state is purposely *not* enforced during initialization in the `OptionalContentConfig` constructor.

 - Printing will now always use the *default* visible layers, rather than using the same state as the viewer (as was the case previously).
   This ensures that the printing-output will correctly take the `Usage` dictionary into account, and in practice toggling of visible layers rarely seem to be necessary except in the viewer itself (if at all).[1]

---
[1] In the unlikely case that it'd ever be deemed necessary to support fine-grained control of optional content visibility during printing, some new (additional) UI would likely be needed to support that case.

web/firefoxcom.js

@@ -258,14 +258,8 @@ if (PDFJSDev.test("GECKOVIEW")) {
             const hasWillPrint =
               pdfViewer.enableScripting &&
               !!(await pdfDocument.getJSActions())?.WillPrint;
-            const hasUnchangedOptionalContent = (
-              await pdfViewer.optionalContentConfigPromise
-            ).hasInitialVisibility;
 
-            result =
-              hasUnchangedAnnotations &&
-              !hasWillPrint &&
-              hasUnchangedOptionalContent;
+            result = hasUnchangedAnnotations && !hasWillPrint;
           } catch {
             console.warn("Unable to check if the document can be downloaded.");
           }