[SDK-1911] Always use UsernamePane when using custom resolver

[stevehobbsdev]

Changes

This PR causes Lock to show the username pane instead of the email pane when connectionResolver is specified. This is so that the validation for that field works as intended when the type of connection can be changed dynamically between those that require a username, and those that don't.

References

Fixes #1732

Testing

Unit tests added to verify functionality of using connectionResolver to force username input.

• This change adds unit test coverage
• This change adds integration test coverage
• This change has been tested on the latest version of the platform/language

Checklist

• I have read the Auth0 general contribution guidelines
• I have read the Auth0 Code of Conduct
• All existing and new tests complete without errors
• All code quality tools/guidelines have been run/followed
• All relevant assets have been compiled
• All active GitHub checks have passed

[lbalmaceda]

@stevehobbsdev Would there be any valid scenario where the pane should be "email" instead of "username" when a resolver is specified?

[stevehobbsdev]

@lbalmaceda There probably is a valid scenario. The problem is that these custom resolvers only run on form submit. So it's difficult to determine at the time when the login form is shown what the best field type is, when it could be changed later. The strategy here is to show a more generic input without formatting validation which works for both cases (email and username), when we know that a custom resolver is being used, as we can't know up-front which type is the best one to use.