Align `label` and `message` props of `coalesceBadge()` with internal `makeBadge()` (#5719)

There is an internal `makeBadge()` function which is called from a few places in the server and from the public `makeBadge()` function which is a light wrapper. (Eventually we want to dogfood the public API: that's the work of #4950, and this helps with it by aligning the interfaces.)

Related to that is #3370, which is about aligning the `serviceData` schema (i.e. the result of `handle()`) with the public `makeBadge()` function.

A legacy quirk of the _private_ `makeBadge()` function is accepting a `text: ['label', 'message']` array instead of separate `{ label, message }` props like the rest of the codebase. `coalesceBadge()` has to translate from `{ label, message }` to `text: ['label', message']`. This removes that bit of indirection.

It also rewrites most of the tests of `coalesceBadge()` to use `.includes()`, providing IMO a slight improvement in readability.