fix(grid): allow filter row to render TD cells

when the filter row renders TH elements, screen readers read its content during browsing

this commit allows the filter row to be rendered as TD elements without visual changes

scss/grid/_layout.scss

@@ -563,7 +563,10 @@
     .k-filter-row {
         line-height: $form-line-height;
 
+        td,
         th {
+            border-width: 0 0 1px 1px;
+            white-space: nowrap;
             padding: $cell-padding-y;
         }
 

scss/grid/_theme.scss

@@ -24,6 +24,7 @@
     .k-grid-content-locked,
     .k-grid-footer-locked,
     .k-grid-header-locked,
+    .k-filter-row > td,
     .k-filter-row > th {
         border-color: $grid-chrome-border;
     }