Re-factor the isPageVisible-handling in the find-controller (PR 10217 follow-up)

The way that this was implemented in PR 10217 has always bothered me slightly, since the `isPageVisible`-method that I introduced there always felt quite out-of-place in the `IPDFLinkService`-implementations.
Hence this is instead replaced by a callback-function in `PDFFindController`, to handle the page-visibility checks. Note that since the `PDFViewer`-constructor always sets this callback-function, e.g. the viewer-component examples still work as-is.

web/pdf_link_service.js

@@ -569,13 +569,6 @@ class PDFLinkService {
     return this.#pagesRefCache.get(refStr) || null;
   }
 
-  /**
-   * @param {number} pageNumber
-   */
-  isPageVisible(pageNumber) {
-    return this.pdfViewer.isPageVisible(pageNumber);
-  }
-
   /**
    * @param {number} pageNumber
    */
@@ -745,13 +738,6 @@ class SimpleLinkService {
    */
   cachePageRef(pageNum, pageRef) {}
 
-  /**
-   * @param {number} pageNumber
-   */
-  isPageVisible(pageNumber) {
-    return true;
-  }
-
   /**
    * @param {number} pageNumber
    */