use pointer cursor for native select when not disabled

Author: Vivian Hu

src/lib/input/input.scss

@@ -152,5 +152,8 @@ select.mat-input-element {
   [dir='rtl'] & {
     background-position: left center;
   }
-}
 
+  &:not(:disabled) {
+    cursor: pointer;
+  }
+}