Introduce `Date`-to-`Instant` and `Instant`-to-`Date` converters

[sbrannen]

Overview

For #35156, we decided to register runtime hints for the java.sql.Timestamp.from(Instant) static factory method, since we want to avoid a direct dependency on optional java.sql types.

However, we can provide explicit support for java.util.Date.from(Instant) and the toInstant() instance methods in java.util.Date and its subtypes.

To achieve that, we should introduce an InstantToDateConverter and a DateToInstantConverter and register them automatically in DefaultConversionService.

Related Issues

• Register runtime hints for Instant-to-Timestamp conversion #35156