[SDK-3537] Credential manager for React Native

[poovamraj]

Changes

We have provided Credentials Manager support for Android and iOS in React Native. The following methods are added

• getCredentials
• saveCredentials
• hasValidCredentials
• clearCredentials

We also return a boolean value from Android API for clearCredentials. This is to be same to our iOS API and Flutter API

This PR is a superset of https://github.com/auth0/react-native-auth0/pull/497 and will have all the changes and reviews from there implemented.

References

https://github.com/auth0/react-native-auth0/issues/476

Testing

• [x] This change adds unit test coverage
• [x] This change has been tested on the latest version of the platform/language or why not

Checklist

• [x] I have read the Auth0 general contribution guidelines
• [x] All existing and new tests complete without errors
• [x] All active GitHub checks have passed

[stevehobbsdev]

👋🏻 Should this be going into master, or vnext?