## 🚀 Feature Proposal

#7753 added basic support for WebAuthn automation in the form of the `addVirtualAuthenticator` and `removeVirtualAuthenticator` methods. Implement the rest of the methods: `addCredential`, `getCredential`, `removeCredential`, `removeAllCredentials`, `setUserVerified`.

## Motivation

Support more WebAuthn use-cases, like logging in with a specific credential, handling user verification failures, and inspecting generated credentials.

## Example

For a page like this

```html
<button id="login">Log in with WebAuthn</button>
<span id="result"></span>
```

```javascript
document.getElmentById("login").addEventListener("click", () => {
  navigator.credentials.get({...}).then(assertion => {
    document.getElementById("result").innerText = "Success!";
  })
});
```

A test could be written like so:

```java
// Set up the virtual authenticator.
HasVirtualAuthenticator virtualAuthenticatorManager = ((HasVirtualAuthenticator) driver);
VirtualAuthenticatorOptions options = new VirtualAuthenticatorOptions();
VirtualAuthenticator authenticator =
    virtualAuthenticatorManager.addVirtualAuthenticator(options);

// New code: inject a credential into the authenticator.
// Without this API the developer would have to generate a credential through
// navigator.credentials.create({...}) on the javascript side and would have less
// control over the resulting PK.
Credential credential = Credential.createNonResidentCredential(...params);
virtualAuthenticatorManager.addCredential(authenticator, credential);

// Assert login successful:
driver.findElement(By.id("login")).click();
WebElement result = driver.findElement(By.id("result"));
new WebDriverWait(driver, 60, 1000).until(
    driver -> !result.getText().equals(""));
assertThat(result.getText()).isEqualTo("Success!");
```
@Override
  public <X> X getScreenshotAs(OutputType<X> outputType) throws WebDriverException {
    Response response = execute(DriverCommand.SCREENSHOT);
    Object result = response.getValue();
    if (result instanceof String) {
      String base64EncodedPng = (String) result;
      return outputType.convertFromBase64Png(base64EncodedPng);
    } else if (result instanceof byte[]) {
      String base64EncodedPng = new String((byte[]) result);
      return outputType.convertFromBase64Png(base64EncodedPng);
    } else {
      throw new RuntimeException(String.format("Unexpected result for %s command: %s",
          DriverCommand.SCREENSHOT,
          result == null ? "null" : result.getClass().getName() + " instance"));
    }
  }
  @Override
  public List<WebElement> findElements(By by) {
    return by.findElements(this);
  }
  @Override
  public WebElement findElement(By by) {
    return by.findElement(this);
  }
  protected WebElement findElement(String by, String using) {
    if (using == null) {
      throw new IllegalArgumentException("Cannot find elements when the selector is null.");
    }
    Response response = execute(DriverCommand.FIND_ELEMENT(by, using));
    Object value = response.getValue();