[api-minor] Add a wrapper around the addLinkAttributes-function, in the API, to the PDFLinkService implementations

This patch helps reduce some duplication, given that we now have a few essentially identical `addLinkAttributes` call-sites in the code-base.
To prevent runtime errors in the Annotation/XFA-layer code, we'll warn if a custom/incomplete `PDFLinkService` is being used (limited to GENERIC builds).

web/interfaces.js

@@ -63,6 +63,13 @@ class IPDFLinkService {
    */
   goToPage(val) {}
 
+  /**
+   * @param {HTMLAnchorElement} link
+   * @param {string} url
+   * @param {boolean} [newWindow]
+   */
+  addLinkAttributes(link, url, newWindow = false) {}
+
   /**
    * @param dest - The PDF destination object.
    * @returns {string} The hyperlink to the PDF object.