[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.

test/driver.js

@@ -684,7 +684,9 @@ class Driver {
             }
 
             task.pdfDoc = doc;
-            task.optionalContentConfigPromise = doc.getOptionalContentConfig();
+            task.optionalContentConfigPromise = doc.getOptionalContentConfig({
+              intent: task.print ? "print" : "display",
+            });
 
             if (task.optionalContent) {
               const entries = Object.entries(task.optionalContent),

test/pdfs/bug1826783.pdf.link

@@ -0,0 +1 @@
+https://bugzilla.mozilla.org/attachment.cgi?id=9327375

test/test_manifest.json

@@ -4016,6 +4016,23 @@
     "lastPage": 5,
     "type": "eq"
   },
+  {
+    "id": "bug1826783-display",
+    "file": "pdfs/bug1826783.pdf",
+    "md5": "93e706efee15dd7b32d32d66f15a3ea2",
+    "rounds": 1,
+    "link": true,
+    "type": "eq"
+  },
+  {
+    "id": "bug1826783-print",
+    "file": "pdfs/bug1826783.pdf",
+    "md5": "93e706efee15dd7b32d32d66f15a3ea2",
+    "rounds": 1,
+    "link": true,
+    "type": "eq",
+    "print": true
+  },
   {
     "id": "issue8586",
     "file": "pdfs/issue8586.pdf",