Optimize CreditDisplay

For a 2K fullscreen Mount Everest view, the profile for `CreditDisplay.add` went from:
```
1.51% total
```
to
```
0.33%
```
We could improve and simplify `CreditDisplay` a lot more, but this at least drops it to something more reasonable on the profile.
Using an array instead of an object will produce (slightly) shorter keys.