Fix previews in MessageCard Composable

[MozillaNoah]

The MessageCard Composable currently takes in a Nimbus-driven object which breaks the previews, when the Composable really only needs three elements:

1. Title text
2. Message text
3. Button text

The message: Message parameter should be refactored so only the actual text is passed-in.

@Composable
fun MessageCard(
    titleText: String?,
    messageText: String?,
    buttonText: String?,
    onClick: () -> Unit,
    onCloseButtonClick: () -> Unit,
) {
   ...
}

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