Fix: changed `DateField` exposed typing information from `DateValue` to `string` (resolves 66)

[helloLilyX]

• Also removed unused imports in Form components

[helloLilyX]

Typo in my second commit message. Cleaned up DateField not LookupField

[helloLilyX]

Observation:

• In our RHF example on Storybook, DateField has a defaultValue = "08-14-1989". The value attribute in its hidden <input> element changed accordingly as we expected when I put in a valid date. However, when I deleted the entire date part (DatedField showed as 8/dd/1989), the value attribute in the hidden <input> element changed to "08-14-1989" (which is the default value). Then I clicked on the "Submit" button, FieldValue had "dateField: null".

Shouldn't the value attribute in the hidden <input> element have undefined and trigger an error for DateField in RHF?

I currently have <input aria-hidden="true" name={props.name} type="text" value={state.value?.toString()} /> which should set the value attribute in the hidden <input> element to undefined when state.value is undefined(state.value works fine), however, it showed as `"08-14-1989".

For the RHF part, I have onChange: (value: DateValue | undefined) => onChange && onChange(value?.toString()) sets "DateField": undefined correctly (It's not printed out under FieldValue because {formData ? JSON.stringify(formData, undefined, 2) : 'Submit the form to view FieldValues'} is used to show formData, but undefined doesn't exist in JSON(null does)).

My guess: does <input> have a setting that would convert its undefined or null value to its default value?

[helloLilyX]

Confusion in my version:

• In the "Controlled Value" example, after I deleted the time part, the text below showed "Your date is: undefined" which means value had undefined. However, no matter what the time part was before, it became "14" (DateField showed as 8/14/1989). I console.loged state, and state.value had the DateValue version of 8/14/1989. If I deleted three more times on the date part, it would eventually have 8/dd/1989.

[helloLilyX]

Also there's a type error in form.stories.tsx:

Ignore this, I saw it was recently fixed in version 5.0.0-alpha.18