Previously, one-time donations were on one screen and monthly donations
were on another. Now, they're on a single screen with a picker.
Most of the interesting changes are in `DonateViewController`.
Other things of note:
- There are some new TODOs here for existing bugs I didn't fix. For
example, one-time donations don't do so well if there are any problems
at all.
- Even though we only support Apple Pay, there's code that alludes to
additional payment methods. For example,
`DonateChoosePaymentMethodSheet`. We'll expand on this in the future.
- Users should only be able to select currencies that the server
supports. For example, you shouldn't be able to select EUR if the
server doesn't support euros. This wasn't working correctly before,
but is fixed here.
We already fixed one part, where users could change to an unsupported
currency (see dab02f30ae). However, if
your _default_ currency is unsupported and you didn't change it,
that's no good. This is unlikely for most users but could happen.
I fixed this by changing it from (effectively)
`Locale.current.currencyCode ?? "USD"`, which might not be supported,
to a preference list, choosing the first one the server likes.
- I skip animations if the Reduce Motion setting is enabled.
- On the donation screen, the logic for the preview badge has changed
slightly. If you already have a badge, we'll always use that.
