feat(filtering): moving the styles from dropdown to grid component

Author: MPopov

projects/igniteui-angular/src/lib/core/styles/components/grid/_grid-component.scss

@@ -542,6 +542,10 @@
         @extend %igx-grid__filtering-cell-indicator--hidden !optional;
     }
 
+    @include e(filtering-row-dropdown-items) {
+        @extend %igx-grid__filtering-row-dropdown-items !optional;
+    }
+
     @include e(filtering-row) {
         @extend %igx-grid__filtering-row !optional;
     }

projects/igniteui-angular/src/lib/core/styles/components/grid/_grid-theme.scss

@@ -2396,6 +2396,11 @@
         }
     }
 
+    %igx-grid__filtering-row-dropdown-items {
+        display: flex;
+        align-items: center;
+    }
+
     %igx-grid__filtering-row--cosy {
         height: map-get($grid-header-height, 'cosy');
     }