`date_select` helper `:with_css_classes` option now accepts a hash of strings
for `:year`, `:month`, `:day`, `:hour`, `:minute`, `:second` that will extend
the select type with the given css class value.

```erb
<%= f.date_select :birthday, with_css_classes: { month: "my-month", year: "my-year" } %>
```

```html
<select id="user_birthday_3i" name="user[birthday(3i)]">…</select>
<select id="user_birthday_2i" name="user[birthday(2i)]" class="my-month">…</select>
<select id="user_birthday_1i" name="user[birthday(1i)]" class="my-year">…</select>
```

Optional, add global `html_options` to modify every select tag in the set.

```erb
<%= f.date_select :birthday, with_css_classes: { month: "my-month", year: "my-year" }, { class: "my-date optional" } %>
```

Supported DateHelper methods: `select_day`, `select_month`, `select_year`,
`select_hour`, `select_minute`, `select_second`, `select_datetime`, `select_time`,
`time_select`, `date_select` and `datetime_select`.

`:with_css_classes` option was added to the `date_select` with #7975.