In order to use a hook that will get user mention candidates that are resolved, we need to first extract the logic to compute user chat mention candidates outside of the class component. There are two steps to this:

1. Lift the selectionState out of the class component
2. Move the computation logic out of the class component

This diff just covers step 2. We should now be able to refactor getMentionTypeaheadUserSuggestions into a hook that will allow for @ mentioning ENS users by their name.

Addresses https://linear.app/comm/issue/ENG-6112/update-native-chat-input-bar-to-make-it-easier-to-use-hooks

Depends on D10385

Once again confirmed that there were no regressions introduced by this changed. I also added some console.log statements for suggestions both off master and this diff, and made sure that I didn't notice any additional re-renderings caused by this change.