fix(): regain focus on mouse move

backports #8179

fixes #8177 caused by #3759
and fixes #3661 that was the motivation for #3759

This issue was caused because the hiddenTextarea looses focus after mousedown.
So I have added a focus call in mousemove that fixes both issues.

src/mixins/canvas_events.mixin.js

@@ -152,14 +152,6 @@
         _target && target.fire('mouseout', { e: e });
       });
       this._hoveredTargets = [];
-
-      if (this._iTextInstances) {
-        this._iTextInstances.forEach(function(obj) {
-          if (obj.isEditing) {
-            obj.hiddenTextarea.focus();
-          }
-        });
-      }
     },
 
     /**

src/mixins/itext_behavior.mixin.js

@@ -386,6 +386,9 @@
         return;
       }
 
+      // regain focus
+      document.activeElement !== this.hiddenTextarea && this.hiddenTextarea.focus();
+
       var newSelectionStart = this.getSelectionStartFromPointer(options.e),
           currentStart = this.selectionStart,
           currentEnd = this.selectionEnd;