frontend: alerter: improve long message support

Current behaviour

1. #1083 added truncation with ellipses, but that means long messages can only be viewed as tooltips.
2. MAVLink STATUSTEXT messages (the source of most of our alerter alerts) are currently sent immediately to the alerter, even if only partially formed

Expected or desired behaviour

1. Ideally long messages would either wrap over multiple lines, or at least support some kind of auto-scrolling behaviour to allow reading them when they're visible (like in our ScrollingText component).
2. The message definition has a limited character length, but there's a specified splitting and sequence re-combination mechanism, to allow sending longer messages, and it would be good if we could support that properly

Prerequisites

• I have checked to make sure that a similar request has not already been filed or fixed.