Handtool: Remove focus from previous node on click

"This commit fixes the issue that a focused element cannot lose
focus when the draggable element is clicked."
https://github.com/Rob--W/grab-to-pan.js/commit/11c368f97cebe19

Steps to reproduce/verify:
1. Enable the hand tool (e.g. by using the H shortcut)
2. Click on the Page number input.
3. Click or drag the PDF canvas.
4. Observe that the page number input is still focused.
   Consequently, the hand tool cannot be disabled using the H shortcut.

web/grab_to_pan.js

@@ -135,6 +135,11 @@ var GrabToPan = (function GrabToPanClosure() {
       event.preventDefault();
       event.stopPropagation();
       this.document.documentElement.classList.add(this.CSS_CLASS_GRABBING);
+
+      var focusedElement = document.activeElement;
+      if (focusedElement && !focusedElement.contains(event.target)) {
+        focusedElement.blur();
+      }
     },
 
     /**