fix(form): Select disabled styling

Updated the cursor for the Select to be the default cursor instead of
the inherited text cursor while disabled since this mimics the native
`<select>` behavior better.

packages/form/src/select/_mixins.scss

@@ -80,6 +80,10 @@
 
   &--disabled {
     @include rmd-theme(color, text-disabled-on-background);
+
+    // this mimics the native select better since it would show the text icon
+    // without this while disabled
+    cursor: default;
   }
 
   &__value {