Use tabular font for numeric fields

When you’re entering numbers into a field we already add some extra
tracking to make it easier to read.

With this extra tracking the kerning looks a bit more even with the
tabular, not lining numbers. This makes sense because tabular numbers
are designed to be used where the content is numeric-only. Lining
numbers (the default) are more appropriate for numbers that are used in
passages of text.

app/assets/stylesheets/components/textbox.scss

@@ -56,6 +56,7 @@
 }
 
 .extra-tracking .form-control {
+  @include core-19($tabular-numbers: true);
   padding-left: 5px;
   letter-spacing: 0.04em;
 }