fix(ESF): horizontal scrollbar

Closes #7865

Author: MPopov

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

@@ -22,6 +22,7 @@
         flex-grow: 1;
         box-shadow: igx-elevation($elevations, 12);
         overflow: auto;
+        min-width: rem(320px);
     }
 
     %grid-excel-filter--inline {
@@ -58,9 +59,8 @@
         display: flex;
         flex-direction: column;
         height: 100%;
-        width: 320px;
-        min-width: 320px;
         background: --var($theme, 'filtering-row-background');
+        // TODO The border-radius should not be hardcoded.
         border-radius: 4px;
 
         @include igx-button-group(igx-button-group-theme(