Date range field type, widgets, formatters

Problem/Motivation

The time has come where I think I need this. We shouldn't need to rely on the datetime module if we can get this working in custom_field. Basically need to have the ability to set a Date start and Date end with widgets, formatters, etc...

Proposed resolution

Extend the date field logic we already have.

Remaining tasks

• Storage: same option for datetime type.
• Widgets: Extend same widgets to accommodate extra field
• Formatters: Extend same formatters to accommodate extra field
• JSON:API support
• GraphQL compose support
• Feeds integration
• Views support
• Flex form display support