use pointer cursor for native select when not disabled (#13184)

Author: vivian-hu-zz

src/lib/input/input.scss

@@ -153,6 +153,10 @@ select.mat-input-element {
     border: 0;
   }
 
+  &:not(:disabled) {
+    cursor: pointer;
+  }
+
   // As a part of its user agent styling, IE11 has a blue box inside each focused
   // `select` element which we have to reset. Note that this needs to be in its own
   // selector, because having it together with another one will cause other browsers