Add definition for `default()` method signature (#32532)
Add definition for `default()` method signature (#32532)

* Add definition for `default()` method signature

Per the documentation (https://github.com/jquense/yup#mixeddefault-any) a call to `default` with no value should return an instance of the type that the schema describes, rather than the schema itself.

* Update index.d.ts

Make `value` no longer optional in the `default` definition

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