Prefer named exports over default exports

### Background

We're doing away with default exports in favor of named exports. For some background on the issue, see the following blog posts:

- https://www.codingzeal.com/posts/developer-dark-arts-default-exports
- https://betterprogramming.pub/understanding-the-difference-between-named-and-default-exports-in-react-2d253ca9fc22

### Process
**This should happen piecemeal, rather than all-at-once.** It will be too much work, too big a change, and too risky to change all our default exports at the same time. Instead, we should clean up exports as we see them.

The analogy I used is: you can go to the beach to clean it up and pick up trash, or you can go to the beach to hang out, play in the ocean, have a good time, and then on the way back to the car, grab a couple of pieces of trash because every little bit helps. What we should do is akin to picking up a couple pieces of trash on the way back to the car.

If you're modifying a file and you notice it has a default export, if it's not too big a task, change it to a named export and change the files that import that module as part of your larger change. If you're creating a new file, go with named exports from the start.

Obviously, we expect you to use your judgement here. If you're changing one word in a file that has a default export, but there are 30 files that import from it, consider making a follow-up PR to change that default export, or writing a ticket to address it if you can't follow up on it. If you're refactoring a component that has a default export and is imported in two places, it's probably a good idea to just make the change as part of that larger PR (maybe as a separate commit).

### Acceptance Criteria
- Your PR has `Helps with #6007` or `Connects #6007` when it removes a default export so that it can be linked to this issue
- When the only default exports we have are the exceptions to the rule (or we have none at all), we can close this ticket.