Expose error message setter on default error state

[AchrafAmil]

When using the default error state, one can switch to it using showError { myRetryCallback() } setting thereby a click listener on the retry button.

But, unlike the default error state retry button, there is no way to access the default error state message textView.

Suggestion: add a showError("there was a glitch, try again") { retry() } extension function.

[sjcqs]

Good idea 😄