Check handle as you type (#8601)

* check handle as you type

* metrics

* add metric types

* fix overflow

* only check reserved handles for bsky.social, fix test

* change validation check name

* tweak input

* move ghosttext component to textfield

* tweak styles to try and match latest

* add suggestions

* improvements, metrics

* share logic between typeahead and next button

* Apply suggestions from code review

Co-authored-by: surfdude29 <149612116+surfdude29@users.noreply.github.com>

* update checks, disable button if unavailable

* convert to lowercase

* fix bug with checkHandleAvailability

* add gate

* move files around to make clearer

* fix bad import

* Fix flashing next button

* Enable for TF

---------

Co-authored-by: surfdude29 <149612116+surfdude29@users.noreply.github.com>
Co-authored-by: Hailey <me@haileyok.com>
Co-authored-by: Eric Bailey <git@esb.lol>

src/screens/Signup/BackNextButtons.tsx

@@ -9,7 +9,7 @@ import {Loader} from '#/components/Loader'
 export interface BackNextButtonsProps {
   hideNext?: boolean
   showRetry?: boolean
-  isLoading: boolean
+  isLoading?: boolean
   isNextDisabled?: boolean
   onBackPress: () => void
   onNextPress?: () => void