Add equatable conformance to UncheckedSendable when value is equatable

[maxgoedjen]

This change makes it easier to have unchecked types (eg, Color, Image) in State objects.

• swift test passed without issue.

[tgrapperon]

It seems to me that Equatable is reasonable, given that one may also encounter this type in Action cases.
Isn't the compiler capable of inferring the implementation though?

[stephencelis]

Thanks! This is definitely missing functionality. We'll merge as is and explore if we can simplify it per @tgrapperon's recommendation, as well as introduce other missing conditional conformances.

[maxgoedjen]

Yep, right you are on the automatic synthesis @tgrapperon. Thanks for merging + extending 🙏 @stephencelis.