[api-minor] Add a basic AbortSignal.any polyfill in PDF.js legacy builds

This is an admittedly very basic polyfill, to allow us to remove a bunch of inline feature testing, that I've thrown together based on reading https://developer.mozilla.org/en-US/docs/Web/API/AbortSignal/any_static and related MDN articles.

Compared to PR 19218 it's obviously much more "primitive", however the implementation is simple and it doesn't suffer from any licensing issues (since I wrote the code myself).

src/shared/util.js

@@ -1172,6 +1172,37 @@ if (
   };
 }
 
+if (
+  typeof PDFJSDev !== "undefined" &&
+  !PDFJSDev.test("SKIP_BABEL") &&
+  typeof AbortSignal.any !== "function"
+) {
+  AbortSignal.any = function (iterable) {
+    const ac = new AbortController();
+    const { signal } = ac;
+
+    // Return immediately if any of the signals are already aborted.
+    for (const s of iterable) {
+      if (s.aborted) {
+        ac.abort(s.reason);
+        return signal;
+      }
+    }
+    // Register "abort" listeners for all signals.
+    for (const s of iterable) {
+      s.addEventListener(
+        "abort",
+        () => {
+          ac.abort(s.reason);
+        },
+        { signal } // Automatically remove the listener.
+      );
+    }
+
+    return signal;
+  };
+}
+
 export {
   _isValidExplicitDest,
   AbortException,