Add rtl resizing and navigation implementation

Author: yuriy-fix

src/vaadin-grid-column-resizing-mixin.html

@@ -56,7 +56,9 @@
           var style = window.getComputedStyle(targetCell);
           var minWidth = 10 + parseInt(style.paddingLeft) + parseInt(style.paddingRight) + parseInt(style.borderLeftWidth)
             + parseInt(style.borderRightWidth) + parseInt(style.marginLeft) + parseInt(style.marginRight);
-          column.width = Math.max(minWidth, targetCell.offsetWidth + e.detail.x - targetCell.getBoundingClientRect().right) + 'px';
+          const maxWidth = targetCell.offsetWidth + (this.__isRTL ? targetCell.getBoundingClientRect().left - e.detail.x :
+            e.detail.x - targetCell.getBoundingClientRect().right);
+          column.width = Math.max(minWidth, maxWidth) + 'px';
           column.flexGrow = 0;
         }
         // Fix width and flex-grow for all preceding columns

src/vaadin-grid-keyboard-navigation-mixin.html

@@ -139,10 +139,10 @@
       let dx = 0, dy = 0;
       switch (key) {
         case 'ArrowRight':
-          dx = 1;
+          dx = this.__isRTL ? -1 : 1;
           break;
         case 'ArrowLeft':
-          dx = -1;
+          dx = this.__isRTL ? 1 : -1;
           break;
         case 'Home':
           dx = -Infinity;