[feat] Export the Calendar component as standalone from DatePicker

[dzole0311]

Does your feature request relate to a specific USWDS component?

Yes, it relates to the Calendar component within the DatePicker: https://github.com/trussworks/react-uswds/blob/5307046f9471215b04a9b33f6150ffab8b71aacc/src/components/forms/DatePicker/Calendar.tsx

What USWDS Version is this feature present in?

All versions.

Is your feature request related to a problem? Please describe.

Currently, it is not possible to use the Calendar component independently without importing the entire DatePicker component. To conditionally render or toggle the Calendar, we must simulate a click on the usa-date-picker__button within the DatePicker (e.g., querySelector('button.usa-date-picker__button').click()), which is a hacky and unreliable approach.

Describe the solution you'd like

Please export the Calendar component as a standalone component, allowing it to be imported and used independently of the DatePicker.

Additional context

N/A