Bug 1802353 - Expose the pref 'apz.allow_zooming' in pdf.js r=pdfjs-reviewers,marco

This way it'll be possible to enable/disable pinch-to-zoom feature in pdf.js.

Differential Revision: https://phabricator.services.mozilla.com/D163072

toolkit/components/pdfjs/content/PdfStreamConverter.jsm

@@ -377,6 +377,10 @@ class ChromeActions {
     return !!prefBrowser && prefGfx;
   }
 
+  supportsPinchToZoom() {
+    return getBoolPref("apz.allow_zooming", true);
+  }
+
   supportedMouseWheelZoomModifierKeys() {
     return {
       ctrlKey: getIntPref("mousewheel.with_control.action", 3) === 3,