[Authenticator] Improve code entry UX

### Before opening, please confirm:

- [x] I have [searched for duplicate or closed issues](https://github.com/aws-amplify/amplify-ui-android/issues?q=is%3Aissue+).

### Which UI component is this feature-request for?

Authenticator

### Please include any relevant guides or documentation you're referencing

_No response_

### Please describe your feature-request in detail.

Authenticator currently uses a plain text box for collecting confirmation codes, such as if a user has SMS MFA enabled, or for collecting email validations post-signup.

This works fine but it isn't very nice looking. Most code collection UIs use discrete boxes to collect the code, similar to the following image:


This feature request proposes introducing a new type of input `FieldConfig.Code` specifically for collecting validation codes that will implement a UI similar to to the above.

### Initialization steps (if applicable)

_No response_

### Code Snippet

```java
// Put your code below this line.

```

### amplifyconfiguration.json

_No response_

### Additional information and screenshots

_No response_

Start by reading the Authenticator component and its FieldConfig API, focusing on how confirmation and validation codes are currently collected. The issue's requested outcome is a new FieldConfig.Code input with discrete code-entry boxes for SMS MFA and post-signup email validation.

Written by the indexing model from the issue text.