[native] Connect selection state with TextInput state in KeyserverSelection

Summary:
Three changes:

1. When the "Ashoat" option is selected, we blur the custom option's TextInput
2. When the custom option's TextInput is focused, we select that option
3. When the custom option is selected, we focus that TextInput if it's empty

Test Plan:

(I also tested the same thing on Android)

Reviewers: ginsu, atul

Reviewed By: atul

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D7592