iOS keeps track of the last-used skin tone modifiers for every
reaction emoji you use. Before reactions were customizable, this
applied to the default set of reactions as well: if you went into the
full picker to select a light-skinned thumbs-up, the short picker
would also have a light-skinned thumbs-up from then on, and if you
changed to dark skin or back to "default" (yellow in our font), the
short picker would be updated again.
However, this is *not* how the customized reactions sync'd through
storage service work; those have skin tone modifiers "baked in", so to
speak. These reactions weren't being treated as valid because they
weren't "base" emoji that could have a skin tone applied to them.
This PR changes things so that there are now two possible states:
- You have never customized your reactions on any platform. In this
case, skin tones continue to follow your most recent choice for that
emoji from the full picker.
- You *have* customized your reactions, in which case it's assumed
they already have the skin tones you want. This even allows you to
have multiple reactions in your default set with the same base emoji
but different skin tones.
Further commits will remove the special nature of the first state.
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