The `:include_blank` option of various `<select>`-related helpers causes
an `<option>` element with no content to be rendered. However, the
[HTML spec] says that unless an `<option>` element has a `label`
attribute (which must be non-empty), its content must be "Text that is
not inter-element whitespace."
In #24923, this issue was addressed for `select_tag` by adding a `label`
attribute to the `<option>`. This commit addresses the issue in the
same manner for `FormBuilder#select` and various date / time select
helpers.
[HTML spec]: https://html.spec.whatwg.org/multipage/form-elements.html#the-option-element