Prevent keyboard interaction with form elements in PresentationMode (issue 12232)

This uses the relatively new `HTMLElement.inert` property, see https://developer.mozilla.org/en-US/docs/Web/API/HTMLElement/inert for additional information. The only "problem" is that this isn't yet available in all Firefox channels, but until https://bugzilla.mozilla.org/show_bug.cgi?id=1764263 is fixed we're no worse off than before.

web/interfaces.js

@@ -61,6 +61,11 @@ class IPDFLinkService {
    */
   set rotation(value) {}
 
+  /**
+   * @type {boolean}
+   */
+  get isInPresentationMode() {}
+
   /**
    * @type {boolean}
    */