Add support for searching emoji and reactions

[innovate-invent]

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Description

Is it quite convenient to react to messages I want to refer back to with specific emoji (such as 📌).

This PR adds the Unicode emoji character class to the message indexing filter, including emoji in messages in the search index.
It also includes reaction emoji as a separate column in the search index.

I tested adding, changing, and removing reactions to a message and the interaction with the search results. I also tested deleting a message with a reaction.

I am not clear how Signal updates its database after a schema change. This CR works for new installs but fullyResetTables needs to be called in the event the app is being updated.

If this is accepted I intend to cut another PR that will allow multiple different reactions to a message from the same sender*.

[innovate-invent]

I just realized I am missing LIMIT 1 on the insert and delete queries, fixing that and re-testing..

[greyson-signal]

I don't think we want to add searching for reactions just yet, but adding the character classes for emoji looks very useful. I don't know if we want S*, but Sc and So seem like they would cover all of our needs! I'll look at taking that specific part and adding the database migration, and will give you co-authorship. Thanks!

[innovate-invent]

Can you elaborate on why searching reactions shouldn't be added? It seems like a valuable feature.

[greyson-signal]

I'd want to consider what the proper UX would be

[innovate-invent]

What would motivate that consideration?