Datetime module needs a view field plugin for its field types

Currently, the datetime module does not define any views/field plugins with @ViewsField(...) tag in them.

There are already plugins for argument, filter and sort.

Views field is useful when writing custom modules that use the Datetime module.

One example is importing a custom base table by implementing a hook_views_data()`. When the table contains a SQL date field, formatted as YYYY-MM-DD, using a datetime views field plugin would be very useful.

The workaround for the case described above is to add a calculable field in SQL query which converts that date field to a unix timestamp field, and using the standard date field handler available in Drupal core.